M720 60mm High-Explosive Mortar

Ordnance Overview

The M720 60mm High-Explosive (HE) Mortar Round is a precision indirect-fire munition serving as the primary combat round for the U.S. military’s M224 60mm mortar system. Adopted in the 1970s, the M720 represents a sophisticated balance of lethality, portability, and reliability designed for infantry support at the company and platoon level. Weighing approximately 1.4 kilograms (3.1 pounds) complete with fuze, the M720 delivers a 0.68-kilogram (1.5-pound) Composition B explosive charge to ranges exceeding 3,500 meters, creating a lethal fragmentation and blast zone with a kill radius of 5-7 meters and casualty-producing effects extending to 20-30 meters. The round features a distinctive teardrop-shaped high-explosive body, a cylindrical tail boom containing the propellant system, and stabilizing fins that deploy upon firing. The M720’s point-detonating (PD) fuze ensures reliable detonation upon impact with the target, making it highly effective against personnel in the open, light fortifications, and soft-skinned vehicles. As a man-portable indirect-fire weapon that can be rapidly deployed and employed, the M720 provides infantry units with immediate, responsive fire support without requiring heavy weapons or vehicle transport.

Country/Bloc of Origin

• Country: United States of America
• Development Period: 1970s
• Official Adoption: Mid-1970s
• Development Agency: U.S. Army Armament Research, Development and Engineering Center (ARDEC), Picatinny Arsenal, New Jersey
• Current Status: Standard issue across all U.S. military branches with 60mm mortar systems
• Mortar System: M224 60mm Lightweight Company Mortar System (adopted 1978)
• Successor To: M49A3 60mm HE mortar round (Korean War/Vietnam era)
• International Distribution: Supplied to NATO allies and partner nations through Foreign Military Sales

Ordnance Class

• Type of Weapon: Indirect-fire high-explosive mortar projectile
• Primary Role: Anti-personnel fragmentation and blast munition
• Secondary Roles: Light fortification suppression, soft vehicle engagement, area denial
• Delivery Method: Muzzle-loaded, smooth-bore, high-angle indirect fire
• Mortar System: M224 60mm lightweight mortar
• Caliber: 60mm (2.36 inches)
• Activation: Point-detonating (PD) impact fuze
• Category: Indirect-fire explosive ordnance

Ordnance Family/Nomenclature

Official Designations

• Primary Designation: M720 High-Explosive (HE) Mortar Round, 60mm
• Complete Nomenclature: Cartridge, 60mm, HE, M720
• NSN (NATO Stock Number): 1315-01-109-6321
• Federal Supply Class: 1315 (Ammunition, Mortar)
• Fuze Designation: M935 Point-Detonating (PD) Fuze

M224 60mm Mortar Ammunition Family

The M720 is one round in a complete family of 60mm ammunition designed for the M224 mortar system:

High-Explosive Variants:

• M720 HE – Standard high-explosive fragmentation round (primary combat round)
• M768 HE – Extended-range version with rocket assist (rarely used, complex)
• M1061 HE – Modern improved fragmentation variant with enhanced lethality

Illumination:

• M721 Illumination – Parachute flare for battlefield illumination (650,000 candlepower, 60 seconds burn time)

Smoke:

• M722 White Phosphorus (WP) – Screening smoke and incendiary effects
• M713 Red Phosphorus (RP) – Screening smoke (less incendiary effect than WP)
• M715 Smoke (Green) – Visible smoke for marking targets
• M716 Smoke (Yellow) – Visible smoke for marking targets

Practice and Training:

• M50A2 Practice Round – Inert training round matching M720 ballistics
• M769 Practice Round – Short-range practice round for training

Special Purpose:

• M302 Infrared Illumination – Night vision-compatible illumination
• M83 Illumination (older type, being phased out)

Related Mortar Systems and Calibers

Other U.S. Mortar Systems:

• 81mm M821 HE – Medium mortar, larger and more lethal than 60mm
• 120mm M933 HE – Heavy mortar, vehicle-mounted
• M224 Mortar System – Complete weapon system firing M720

Historical Predecessors:

• M49A3 60mm HE – Vietnam-era 60mm round (older design)
• M69 60mm HE – Earlier variant
• M302 60mm WP – Historical smoke round

International Equivalents

NATO Allies:

• Many NATO nations use compatible 60mm mortar ammunition
• British L41A1 HE – Similar 60mm HE round
• French MO-60-HE – French 60mm equivalent

Non-NATO:

• Soviet/Russian 82mm – Different caliber but similar role
• Chinese Type 67-1 60mm – Similar concept, different specifications

Common Names and Terminology

• “60 mike-mike” (military slang for 60mm)
• “M720” (standard designation)
• “60mm HE” (generic reference)
• “Sixty mortar round” (informal)
• “Light mortar round” (distinguishing from 81mm/120mm)

Hazards

Primary Hazards

Fragmentation (PRIMARY LETHAL MECHANISM):

The M720 is fundamentally a fragmentation munition designed to produce high-velocity steel fragments that kill or incapacitate personnel in the open.

Fragment Production:

• Steel Body Construction: Approximately 2-3mm thick high-strength steel casing
• Fragment Count: Produces 300-500+ steel fragments upon detonation
• Fragment Velocity: Initial velocity approximately 1,200-1,500 meters per second (3,900-4,900 fps)
• Fragment Weight Range: Individual fragments 1-15 grams (highly variable)
• Fragment Shape: Irregular, jagged steel pieces with sharp edges

Lethal and Casualty Zones:

Kill Radius:

• 5-7 meters (16-23 feet) – high probability of death or incapacitation
• Personnel in the open within this radius have >50% chance of serious injury or death
• Multiple fragment impacts typical within kill zone

Effective Casualty Radius:

• 20-30 meters (65-100 feet) – significant probability of injury
• Wounds requiring medical attention likely
• Single or few fragment impacts expected

Maximum Fragment Range:

• 100-150 meters (330-490 feet) – fragments can travel this far
• Lethality decreases significantly beyond casualty radius
• Fragments retain enough energy to cause injury at extended ranges

Fragment Characteristics:

• Penetrate soft tissue easily within 30 meters
• Can penetrate light cover (wooden structures, thin sheet metal, vegetation)
• Limited effectiveness against hard cover (concrete, earthen berms, thick steel)
• May defeat soft body armor at close range (<20 meters)
• Hard armor (ceramic/steel plates) generally stops fragments

Blast Overpressure (SECONDARY HAZARD):

Explosive Fill:

• Composition B: 680 grams (1.5 pounds)
• Composition: 60% RDX, 39% TNT, 1% wax
• Detonation Velocity: ~7,800 m/s (25,600 fps)

Blast Effects:

• Within 5 meters: Significant blast overpressure
  • Can cause barotrauma (lung damage)
  • Eardrum rupture likely
  • Internal organ damage possible
  • Concussive effects even behind light cover
• 5-15 meters: Moderate blast effects
  • Temporary hearing loss
  • Disorientation and stunning
  • Possible minor internal injuries
• 15+ meters: Minimal blast effects in open terrain

Enclosed Spaces:

• Blast overpressure dramatically amplified in bunkers, buildings, trenches
• Can be lethal at 10-15 meters in confined spaces
• Pressure waves reflect off walls, compounding effects

Impact and Fuze Hazards

Point-Detonating (PD) Fuze:

M935 Fuze Characteristics:

• Type: Super-quick (SQ) point-detonating
• Arming Distance: 5-15 meters from muzzle (safety feature)
• Function: Detonates on impact with ground, structures, or obstacles
• Sensitivity: Designed to function on contact with light materials (soil, vegetation, wood)

Fuze Safety:

• Unarmed state: Fuze is safe during handling and loading
• Arming: Setback force during firing (high-G acceleration) arms fuze
• Spin arming: Rotation during flight completes arming sequence (fins create spin)
• Safety features: Cannot arm if dropped or roughly handled (requires firing acceleration)

Fuze Malfunctions (Rare):

• Dud (failure to detonate): ~1-3% of rounds (fuze or explosive malfunction)
• Blind (fuze malfunction): Round impacts but fuze doesn’t initiate explosive
• Short arms: Premature arming closer than 5 meters (extremely rare, design prevents this)
• Hang fire: Propellant ignites but doesn’t expel round (round stuck in tube)

Propellant Hazards

Propellant System:

The M720’s tail boom contains the propellant charge that launches the round:

Propellant Configuration:

• Primary propellant: Fixed charge in tail boom (single increment)
• Augmenting charges: Optional additional charges attached to tail fins for extended range
• Propellant type: Smokeless powder (nitrocellulose-based)
• Igniter: Percussion primer in base of tail boom

Propellant Hazards:

• Blast from muzzle: Hot propellant gases exit muzzle at high velocity
  • Danger area: 5-10 meters behind muzzle
  • Burns, injuries possible from muzzle blast
• Deflagration: Propellant burns rapidly (does not detonate)
• Fire hazard: Propellant is flammable; damaged rounds may ignite
• Toxic gases: Propellant combustion produces toxic gases (carbon monoxide, nitrogen oxides)

Misfires and Hang Fires:

• Misfire: Round doesn’t fire when dropped down tube
  • Wait 60 seconds before approaching
  • May be delayed ignition (hang fire)
• Squib: Weak propellant burn, round may not clear tube or falls short
  • Extremely dangerous – may detonate in tube or very close to crew

Environmental Hazards

Temperature Sensitivity:

• Propellant: Affected by temperature (hot propellant = longer range; cold = shorter range)
• Explosive: Composition B stable from -40°F to +145°F (-40°C to +63°C)
• Extreme heat (>160°F/71°C): May cause propellant or explosive instability
• Extreme cold (<-50°F/-45°C): Propellant may burn slower, affecting range

Moisture:

• Water exposure: Rounds are moderately water-resistant but not waterproof
• Prolonged immersion may affect propellant reliability
• Fuze may corrode over time if exposed to moisture
• Wet rounds: Should be dried if possible before firing

Impact Sensitivity:

• Generally stable: Not highly impact-sensitive when unfired
• Do not drop rounds – can damage fuze or propellant system
• Damaged rounds must not be fired (risk of malfunction)

Unexploded Ordnance (UXO) Hazards

Dud Rounds:

M720 duds are extremely dangerous:

• Fully armed: Fuze is armed even if round didn’t detonate
• Unstable: Impact may have damaged fuze, making it more sensitive
• Explosive intact: Full 680 grams of Composition B remains
• Fuze sensitivity: May detonate if moved, vibrated, or heated

UXO Procedures:

• Never approach, touch, or move dud rounds
• Mark location from safe distance (minimum 100 meters)
• Evacuate area and establish cordon
• Report to EOD personnel immediately
• Wait for professional disposal (controlled detonation or removal)

Indicators of Dud Status:

• Round impacted ground but didn’t detonate
• Crater or impact mark visible
• Round may be partially buried or lying on surface
• All suspected duds must be treated as armed and dangerous

Training and Handling Hazards

Safe Handling Practices:

• Do not drop rounds – can damage fuze or cause propellant spillage
• Avoid extreme temperatures during storage
• Inspect before firing – check for damage, corrosion, or defects
• Follow proper firing procedures – incorrect procedures can cause accidents
• Maintain safe distances – crew and nearby personnel must be outside danger zones

Common Handling Mistakes:

• Dropping rounds causing fuze or body damage
• Firing damaged or corroded rounds (malfunction risk)
• Improper storage leading to propellant degradation
• Failure to wait after misfire (hang fire risk)

Special Warnings

⚠️ CRITICAL SAFETY INFORMATION:

• The M720 is a HIGH-EXPLOSIVE MUNITION – treat with utmost respect at all times
• Never fire damaged rounds – inspect every round before use
• Maintain 100-meter minimum safe distance for indirect fire operations (crew in protected position)
• Fragments disperse in all directions from impact point – seek hard cover
• Duds are ARMED and will detonate if disturbed – never approach UXO
• Misfires may be hang fires – wait minimum 60 seconds before approaching mortar tube
• Propellant gases are toxic – ensure adequate ventilation during firing
• All personnel must wear appropriate protective equipment during mortar operations
• Weather affects range – hot days increase range, cold days decrease range (adjust fire as needed)
• Impact point prediction is critical – confirm no friendlies in target area before firing

Key Identification Features

Physical Dimensions

Overall Round:

• Total Length: 255mm (10 inches) approximately
• Diameter (Body): 60mm (2.36 inches)
• Total Weight: 1.41 kg (3.1 pounds) complete with fuze
• Weight (body and explosive): ~1.1 kg (2.4 pounds)
• Weight (propellant and tail assembly): ~0.3 kg (0.66 pounds)

High-Explosive Body:

• Length: Approximately 100-120mm (4-4.7 inches)
• Shape: Teardrop/ogive shape (rounded nose, tapering body)
• Material: High-strength steel, 2-3mm wall thickness
• Color: Olive drab with yellow markings

Tail Boom and Fin Assembly:

• Length: Approximately 135mm (5.3 inches)
• Diameter: 60mm (matches body)
• Fins: Six stabilizing fins, folded before firing, deploy after launch
• Fin Material: Steel or aluminum
• Fin Span (deployed): Approximately 100-120mm (4-4.7 inches)

Distinctive Characteristics

Visual Identification Features:

Body Shape:

• Teardrop/ogive profile – rounded nose tapering to cylindrical tail
• Smooth exterior (no segmentation or ribbing)
• Aerodynamic design for stable flight

Color Scheme and Markings:

Body Color:

• Olive Drab (OD) Green or gray-green
• Yellow band around nose (indicates high-explosive filling)
• Yellow markings (stenciled or stamped)

Required Markings (Stenciled in Yellow):

• “M720” – designation
• “HE” – high-explosive indicator
• “60mm” – caliber designation
• “LOT [number]” – production lot number
• Manufacturer code – contractor designation
• Date of manufacture – month/year or lot code
• “COMP B” – explosive type indication

Fuze Markings:

• “M935” – fuze designation (stamped on fuze body)
• Fuze may have additional markings (manufacturer, date)

Propellant Markings:

• Charge indicators on tail boom (if augmenting charges present)
• Increment numbers (0, 1, 2, etc.) indicating propellant load

Assembly Configuration:

Three Main Components (Visible):

1. Fuze (Nose):
   • M935 Point-Detonating Fuze screws into nose
   • Cylindrical brass or steel housing
   • Safety pin or clip visible (removed before firing)
   • Ogive-shaped nose cap
2. High-Explosive Body:
   • Steel cylindrical shell containing Composition B
   • Smooth outer surface
   • Yellow identification band
   • Markings stenciled on body
3. Tail Boom Assembly:
   • Cylindrical tube containing propellant
   • Six folded stabilizing fins
   • Percussion primer in base
   • Optional augmenting charges attached to fin assembly

Fin Assembly Details:

Fins:

• Six fins arranged radially around tail boom
• Folded position: Fins lay flat against tail boom for handling/storage
• Deployed position: Fins extend perpendicular to tail boom after firing
• Function: Stabilize flight and induce spin for fuze arming

Propellant Access:

• Tail boom may have access point for augmenting charges
• Some variants have removable increment charges (added or removed to adjust range)

Material Identification

Body:

• High-strength steel – magnetic, heavy, durable
• Paint finish – textured military enamel (olive drab or gray-green)
• Wall thickness – 2-3mm (designed to fragment upon detonation)

Fuze:

• Brass or steel – threaded housing
• Mechanical components (striker, detonator) inside
• Safety features – mechanical safeties prevent arming until fired

Tail Boom:

• Steel or aluminum – lighter materials for tail section
• Propellant – smokeless powder (not visible externally)
• Primer – brass percussion primer in base

Fins:

• Steel or aluminum – thin material for light weight
• Spring-loaded – deploy automatically when round leaves tube

Internal (Not Visible When Intact):

• Composition B – yellow-orange explosive (visible only if round is damaged)
• Detonator – enclosed in fuze assembly
• Propellant – gray or black granular powder in tail boom

Size Comparison

Relative to Common Objects:

• Length: Approximately same as standard ruler (10 inches)
• Diameter: Slightly larger than golf ball (60mm vs. 43mm)
• Weight: Similar to a large can of soup (3 pounds)
• Overall size: Similar to a small flashlight or large soda bottle

Comparison to Other Ordnance:

• Smaller than 81mm mortar round (M821)
• Larger than 40mm grenade (M203)
• Similar diameter to hand grenade but much longer

Packaging and Transportation

Field Packaging:

• Fiber containers – individual rounds in protective tubes
• Metal canister – some variants use metal storage tubes
• Wooden crates – bulk transport (multiple rounds per crate)

Packing Configuration:

• Typically packed 6-12 rounds per crate
• Fuzes may be packed separately (to be assembled before use)
• Augmenting charges packed with rounds or separately

Carrying Methods:

• Ammunition bearer vest/harness – holds 4-6 rounds in pouches
• Backpacks – specialized mortar ammunition packs
• Ammo cans – metal or plastic containers for transport
• Hand carrying – rounds can be carried individually if needed

Storage Markings:

• Crates marked with “EXPLOSIVE 1.1D” hazard classification
• “60MM MORTAR AMMO” – contents description
• “HE M720” – specific round type
• Lot numbers, date of manufacture, quantity
• UN 0033 – explosive classification code for mortar ammunition

Comparison with Other 60mm Rounds

Visual Distinctions:

M720 (HE) vs. M721 (Illumination):

• M720: Teardrop-shaped body, yellow band, shorter
• M721: Longer cylindrical body, white band, larger overall
• Illumination rounds are distinctively longer

M720 vs. M722 (White Phosphorus):

• M720: Yellow band, OD green body
• M722: Light gray or white band, may have “WP” markings
• WP rounds often have slightly different shape

M720 vs. M50A2 (Practice):

• M720: Yellow band, full weight, explosive markings
• M50A2: Blue body or band, “PRACTICE” markings, similar weight but inert
• Practice rounds have blue identification

Condition Indicators

Good Condition:

• Paint intact, no rust or corrosion
• Fins properly folded and undamaged
• Markings legible
• No dents, cracks, or deformation
• Fuze threads clean and undamaged

Damaged/Suspect Condition:

• Heavy rust or corrosion – indicates moisture exposure
• Dents or deformation – may affect flight or fuze function
• Cracked body – explosive filling may be exposed
• Damaged fins – will affect flight stability
• Missing or damaged fuze – extremely dangerous
• Propellant leakage – visible powder around tail boom
• Discoloration – unusual colors may indicate degradation
• Such rounds must NOT be fired and should be reported for disposal

Fuzing Mechanisms

The M720 employs the M935 Point-Detonating (PD) Super-Quick Fuze, a mechanically-armed, impact-initiated fuzing system designed for reliable ground-burst detonation.

M935 Fuze System

Fuze Type:

• Designation: M935 Point-Detonating Fuze
• Function: Super-quick (SQ) impact detonation
• Arming Method: Mechanical – setback and spin (centrifugal) arming
• Detonation: Immediate upon impact with ground or target
• Category: Point-detonating, mechanically-armed fuze

Fuze Components

External Components:

1. Fuze Body:
   • Cylindrical brass or steel housing
   • Threaded base screws into M720 nose
   • Ogive-shaped nose cap (streamlined for aerodynamics)
2. Safety Features:
   • Mechanical safety – prevents arming until fired
   • Setback lock – released by acceleration during firing
   • Spin safety – released by rotation during flight
   • Dual safety – both setback and spin required to arm

Internal Components:

3. Striker (Firing Pin):
   • Spring-loaded impact striker
   • Locked in safe position by arming mechanisms
   • Strikes detonator on impact when armed
4. Arming Mechanism:
   • Setback component – responds to high-G acceleration during launch
   • Centrifugal component – responds to spin from fin-stabilized flight
   • Mechanical interlocks – ensure fuze cannot arm unless both safeties release
5. Detonator (Primary Explosive):
   • Small explosive charge (lead azide or equivalent)
   • Struck by firing pin upon impact
   • Initiates booster charge
6. Booster Charge:
   • Intermediate explosive (tetryl or RDX)
   • Amplifies detonator output
   • Ensures reliable initiation of main Composition B charge

Arming and Functioning Sequence

Stage 1: Safed Configuration (Storage/Handling/Loading)

• Fuze completely safe
• Mechanical safeties locked in place
• Striker blocked – cannot reach detonator
• No possible accidental detonation from dropping, rough handling, or impact
• Fuze safety pin may be installed (removed before firing in some procedures)

Stage 2: Loading into Mortar

• Round is muzzle-loaded into M224 mortar tube
• Slides down smooth-bore barrel
• Percussion primer in tail contacts firing pin at bottom of tube
• Fuze remains completely safe throughout loading

Stage 3: Firing (Propellant Ignition)

• Firing pin in mortar base strikes percussion primer
• Primer ignites propellant in tail boom
• Propellant burns rapidly – creates high-pressure gas
• Gas pressure propels round out of tube at high velocity (~162 m/s muzzle velocity)

Stage 4: Setback Arming (Launch Acceleration)

• High-G acceleration (thousands of G’s) during launch
• Setback force overcomes first mechanical safety
• Inertial component of arming mechanism moves/unlocks
• First safety released – fuze partially armed
• Occurs within first 5-15 meters of flight

Stage 5: Spin Arming (In-Flight Rotation)

• Stabilizing fins deploy and cause round to spin
• Centrifugal force from rotation
• Spin-sensitive component unlocks (centrifugal mechanism)
• Second safety released – fuze now fully armed
• Arming complete at approximately 5-25 meters from muzzle
• Round now armed and will detonate on impact

Stage 6: Flight Phase (Ballistic Trajectory)

• Round follows high-angle ballistic arc
• Fins stabilize flight
• Fuze remains armed throughout flight
• Typical flight time: 5-30 seconds depending on range
• Round is armed and dangerous throughout flight

Stage 7: Impact and Detonation

• Round impacts ground, structure, or obstacle at high velocity
• Impact drives striker forward against spring resistance
• Striker impacts detonator – creates initial explosion
• Detonator fires – initiates booster charge
• Booster charge detonates – generates shock wave
• Main Composition B charge detonates – high-order explosion
• Total time: microseconds from impact to full detonation
• Steel body fragments into 300-500+ pieces
• Fragments disperse radially at high velocity

Function Summary: Impact → Striker Released → Detonator Fired → Booster → Main Charge → Fragmentation

Fuze Safety Features

Multiple Independent Safeties:

1. Setback Safety (First Safety):
   • Requires high-G acceleration to release
   • Cannot be defeated by dropping, throwing, or rough handling
   • Only firing acceleration sufficient to release
2. Spin Safety (Second Safety):
   • Requires centrifugal force from rapid rotation
   • Fins create spin during flight
   • Cannot be defeated by hand manipulation
3. Dual Safety Requirement:
   • Both safeties must release before fuze is armed
   • Redundancy prevents accidental arming
   • If either safety fails, fuze will not arm
4. Arming Distance:
   • Setback and spin arming require 5-25 meters of flight
   • Safety zone – round will not detonate if dropped in mortar pit
   • Provides crew safety during loading and firing

These safety features make the M720 extremely safe to handle, transport, and load – the fuze cannot arm unless the round is properly fired from a mortar.

Fuze Reliability and Performance

Advantages:

• High reliability: >97% function rate under normal conditions
• Mechanical simplicity: Fewer failure points than electronic fuzes
• Environmental tolerance: Functions reliably in extreme temperatures, moisture, dust
• Instant detonation: Super-quick function on impact (no delay)
• Ground-burst optimization: Designed for surface detonation (maximum fragmentation)
• Safe handling: Cannot arm unless fired (excellent safety record)
• Combat proven: Decades of reliable service

Limitations:

• No adjustable delay: Always detonates immediately on impact
• No air-burst capability: Standard M935 cannot detonate above ground
• Dud rate: ~1-3% of rounds fail to detonate (fuze or explosive malfunction)
• Impact sensitivity: Requires solid impact; soft soil/snow may reduce reliability
• No remote deactivation: Once fired, cannot be remotely destroyed or deactivated

Fuze Malfunctions

Types of Malfunctions:

1. Dud (Complete Failure):

• Frequency: 1-3% of rounds fired
• Causes:
  • Fuze mechanical failure (striker jammed, detonator failure)
  • Explosive degradation or contamination
  • Booster charge failure
  • Moisture infiltration
• Result: Round impacts but does not detonate
• Danger: Fully armed and extremely dangerous – may detonate if disturbed

2. Blind (Partial Function):

• Frequency: Very rare
• Causes: Detonator fires but fails to initiate main charge
• Result: Small detonation (fuze only) but main charge doesn’t explode
• Danger: Main charge intact and unstable

3. Low-Order Detonation:

• Frequency: Rare
• Causes: Degraded explosive, incomplete detonation train
• Result: Explosive deflagrates (burns rapidly) rather than detonates fully
• Danger: Reduced effectiveness; some explosive may remain

4. Premature Arming (Extremely Rare):

• Frequency: Almost never occurs with M935 (safety features prevent)
• Causes: Manufacturing defect, damage to fuze
• Result: Fuze arms prematurely (within arming distance)
• Danger: Could detonate very close to mortar or in tube (catastrophic)

5. Failure to Arm:

• Frequency: <1%
• Causes: Safety mechanisms fail to release, insufficient setback/spin
• Result: Round impacts but fuze is not armed, no detonation
• Danger: Less than dud (fuze not armed) but still contains explosive

Handling Dud Rounds

Critical UXO Procedures:

If an M720 fails to detonate:

1. HALT FIRE IMMEDIATELY – cease all mortar fire
2. Mark impact area from safe distance (minimum 100 meters)
3. Do NOT approach – round is armed and will detonate if disturbed
4. Establish cordon – prevent all personnel from entering area
5. Report to EOD – only explosive ordnance disposal personnel may approach
6. Wait for professional disposal – EOD will conduct controlled detonation or removal
7. Document location – mark on map for future reference

Never:

• Approach a dud round
• Attempt to move, disarm, or inspect a dud
• Assume a dud is “safe” after time passes
• Re-fire mortars toward dud location (may cause detonation)

Alternative Fuze Options

While the M935 is standard, other fuze types exist for specific missions:

Proximity Fuzes (Specialized):

• Electronic fuzes that detonate at preset height above ground
• Increased lethality against personnel
• More complex and expensive than M935
• Used for specific tactical situations

Delay Fuzes (Specialized):

• Detonate after short delay following impact
• Used for penetrating light structures before detonation
• Rare in 60mm systems (more common in larger mortars)

These alternatives are NOT standard with M720 and require specific tactical justification and supply.

History of Development and Use

Origins and Development (1960s-1970s)

Post-Vietnam Lightweight Mortar Requirements:

Following the Vietnam War, the U.S. Army conducted comprehensive analysis of mortar support requirements at the company and platoon level, identifying critical gaps in infantry firepower.

Vietnam Experience:

• M19 60mm mortar (WWII/Korea-era system) remained in service but was heavy and outdated
• Infantry companies needed lighter, more portable indirect fire support
• Existing 60mm ammunition (M49A3 HE, M302 WP) adequate but dated
• Weight was critical issue – infantry needed man-portable systems for jungle/mountain warfare

Development Goals (Early 1970s):

• Develop lightweight mortar system for company-level organic fire support
• Create new ammunition family compatible with lightweight system
• Maximize lethality while minimizing weight
• Ensure reliability in all environmental conditions
• Maintain sufficient range for tactical flexibility (3,000+ meters)

M224 Mortar System Development:

• 1970s: U.S. Army initiated development of M224 60mm lightweight mortar
• Design Features:
  • Total system weight ~21 kg (46 pounds) including baseplate, tube, bipod
  • Can be broken down into three man-portable loads
  • Handheld mode – can be fired from shoulder without bipod for immediate response
  • Conventional mode with bipod and baseplate for sustained fire
• Objective: Replace heavier M19 mortar (46+ pounds for tube alone)

M720 Round Development:

Parallel to M224 development, new ammunition was designed:

Design Requirements:

• Lethality: Match or exceed M49A3 fragmentation effects
• Weight: Minimize for portability (infantry carries rounds on patrol)
• Range: 3,500+ meters maximum
• Accuracy: Improved over predecessor rounds
• Reliability: High function rate in all climates
• Safety: Multiple safety features to prevent accidental detonation

Key Innovations:

• Optimized steel body for consistent fragmentation
• Composition B explosive for maximum blast and fragmentation
• M935 fuze – highly reliable point-detonating design
• Streamlined aerodynamics for extended range and accuracy
• Modular propellant system – optional increment charges for range adjustment

Testing and Evaluation (Mid-1970s):

• Extensive fragmentation testing at Aberdeen Proving Ground
• Lethality analysis against personnel targets
• Environmental testing across temperature extremes
• Reliability testing (function rate, dud rate)
• Safety validation (arming distance, handling safety)
• Comparison with predecessor M49A3 round

Results:

• Improved lethality – 20-30% increase in effective casualty area over M49A3
• Enhanced reliability – >97% function rate achieved
• Weight reduction – lighter than M49A3 while maintaining lethality
• Extended range – maximum range ~3,490 meters vs. 3,000 meters for M49A3
• Superior safety – M935 fuze demonstrated excellent safety record

Official Adoption:

• Mid-to-Late 1970s: M720 officially adopted as standard 60mm HE round
• 1978: M224 mortar system (firing M720) officially adopted
• 1980s: Full fielding to infantry units worldwide
• Rapid replacement of older M49A3 ammunition

Combat Deployment History (1980s-Present)

Initial Fielding (1980s):

Grenada (1983):

• Operation Urgent Fury – first combat use of M224/M720 system
• Rangers and infantry units employed 60mm mortars
• Effective fire support in jungle and urban terrain
• Positive feedback – crews praised accuracy and reliability

Panama (1989):

• Operation Just Cause
• 60mm mortars used extensively in urban warfare
• M720 rounds effective against lightly fortified positions
• Quick-response fire support critical in fast-paced operations

Gulf War Era (1990s):

Operation Desert Storm (1991):

• M224/M720 systems deployed with infantry divisions
• Limited use due to nature of warfare (primarily mechanized, air-dominated)
• When employed, demonstrated excellent reliability in desert environment
• Long-range capability utilized for indirect fire missions

Somalia (1993):

• Operation Gothic Serpent (Battle of Mogadishu)
• Rangers equipped with M224 mortars
• M720 rounds provided critical fire support during intense urban combat
• Accuracy essential in densely populated areas to minimize civilian casualties
• Crews praised responsive fire support capability

Balkans (1990s-2000s):

• Bosnia and Kosovo operations
• Peacekeeping and combat missions
• 60mm mortars provided flexible fire support for dispersed infantry
• M720 rounds used in defensive and limited offensive operations

Global War on Terror (2001-Present):

Afghanistan (2001-2021):

• Operation Enduring Freedom saw extensive M720 employment
• Mountain warfare: 60mm mortars ideal for high-altitude, rugged terrain
• Lightweight: Critical advantage – infantry could carry system on patrols
• Handheld mode: Used for immediate suppressive fire during ambushes

Key Engagements:

• Firebase support: M224 mortars standard defensive weapon at remote outposts
• Patrol support: Infantry squads carried 60mm systems on extended patrols
• Counter-ambush: Immediate indirect fire capability saved numerous lives
• Compound clearing: M720 rounds used to soften Taliban defensive positions

Tactical Effectiveness:

• Responsive fire: Crews could have rounds on target within 1-2 minutes
• Precision: Accuracy adequate for danger-close missions (within 100m of friendlies with adjustment)
• Lethality: Effective against personnel in the open and light structures
• Morale: Infantry valued organic fire support independent of external assets

Iraq (2003-2011):

• Operation Iraqi Freedom – massive M720 employment
• Urban warfare: Fallujah, Ramadi, Baghdad saw extensive 60mm use
• Building suppression: M720 rounds used to suppress enemy in fortified structures
• Counter-mortar: U.S. mortars engaged insurgent mortar positions
• Checkpoint defense: 60mm mortars positioned at security checkpoints

Lessons Learned:

• Urban environments: M720 effective but collateral damage concerns required careful fire control
• Insurgent tactics: Indirect fire essential to counter dug-in insurgents
• Combined arms: Most effective when integrated with air support, artillery, and direct fire

Syria and Iraq (2014-Present):

• Counter-ISIS operations
• Special Operations Forces extensively employed 60mm mortars
• M720 rounds critical for fire support in Syrian cities (Raqqa, Mosul)
• Precision increasingly important due to civilian presence

Current Operations (2020s):

• M720/M224 system remains standard across U.S. Army and Marine Corps infantry
• Deployed in ongoing operations worldwide
• Continuous improvement: Upgrades to ammunition and mortar system ongoing
• M1061 improved HE round introduced (enhanced fragmentation, GPS-guided variants in development)

Production and Distribution

Manufacturing:

• Primary contractors: Multiple U.S. defense contractors over decades
• Current production: Ongoing to replenish expended stocks
• Annual production: Classified but substantial (tens of thousands annually)
• Total production since 1970s: Estimated millions of rounds

Quality Control:

• Rigorous lot acceptance testing
• Statistical sampling: Every production lot tested for reliability
• X-ray inspection for internal defects
• Live-fire testing for function verification
• Strict adherence to military specifications

Foreign Military Sales (FMS):

• M720 supplied to dozens of allied nations
• NATO standardization – many allies use compatible 60mm systems
• Partner nations: Australia, South Korea, Taiwan, Japan, Middle Eastern allies, Latin American partners
• Co-production: Some allies produce M720 under license

Current Inventory:

• U.S. military maintains strategic reserves of millions of M720 rounds
• War reserve stocks at depots worldwide
• Rotating inventory – older ammunition inspected and replaced as needed
• Forward-deployed stocks at overseas bases

Tactical and Doctrinal Impact

Infantry Doctrine Evolution:

Company-Level Organic Fires:

• M224/M720 system provides organic indirect fire to company and platoon level
• Independence from battalion/brigade fire support assets
• Immediate response capability (minutes vs. hours for external fire support)

Tactical Applications:

• Defensive operations: Firebase perimeter defense, counter-attack suppression
• Offensive operations: Suppression before assault, neutralization of enemy positions
• Ambush support: Immediate fire during enemy contact
• Illumination and smoke: Complete family of ammunition supports diverse missions
• Danger-close missions: Can engage targets very close to friendly forces (50-100m) with trained crews

Integration with Modern Systems:

• Digital fire control: Mortar fire direction centers use digital systems (AFATDS)
• GPS navigation: Precise location of mortar and target improves accuracy
• UAV integration: Unmanned aerial vehicles provide target identification and adjustment
• Network-centric warfare: Mortars integrated into overall fire support coordination

Training Emphasis:

• All infantry leaders receive mortar training
• Specialized mortar sections in infantry companies
• Live-fire exercises: Regular training with live M720 rounds
• Safety emphasis: Rigorous safety procedures ingrained through training

Comparison with International Mortars

U.S. M720 vs. Soviet/Russian 82mm:

• M720 (60mm): Lighter, more portable, shorter range (~3.5km), smaller casualty radius
• Soviet 82mm: Heavier, more lethal, longer range (~4-5km), larger casualty radius
• Different doctrine: U.S. favors lightweight company-level assets; Soviet/Russian emphasized heavier battalion-level support

M720 vs. British/NATO 60mm Systems:

• Largely compatible and interoperable
• Similar performance characteristics
• NATO standardization allows ammunition sharing

Advantages of M720 System:

• Lightest weight for its lethality class
• Highly portable – critical for rapid deployment infantry
• Proven reliability – decades of combat use
• Comprehensive ammunition family – HE, illumination, smoke, practice
• Cost-effective – relatively inexpensive per round

Future Developments

Current Modernization:

• M1061 round: Enhanced fragmentation effects (improved lethality)
• Precision-guided variants: GPS-guided mortar rounds in development
  • Improved accuracy
  • Reduced collateral damage
  • Increased first-round hit probability

Technology Integration:

• Digital fuzes: Electronic fuzes with programmable functions (air burst, delay, etc.)
• Sensor-fuzed munitions: Submunitions for anti-vehicle applications
• Networked ammunition: Rounds that communicate with fire control systems

No Replacement Planned:

• M720 (and upgraded variants like M1061) will remain in service for decades
• System proven, effective, and cost-efficient
• Modernization rather than replacement is the approach

Legacy:

• M720 represents over 40 years of reliable service
• Combat-proven in every major U.S. military engagement since 1980s
• Will likely remain standard 60mm ammunition well into 2040s and beyond

Technical Specifications

Explosive Characteristics

Explosive Fill:

• Type: Composition B (RDX/TNT mixture)
• Composition: 60% RDX (cyclotrimethylenetrinitramine), 39% TNT, 1% wax
• Weight: 680 grams (1.5 pounds / 24 ounces)
• Color: Yellow-orange (when visible)
• Detonation Velocity: Approximately 7,800 m/s (25,600 fps)
• TNT Equivalence: ~1.3:1 (Comp B is more powerful than TNT)
• Explosive Energy: ~5.3 MJ/kg

Blast Effects:

• Peak Overpressure: >50 psi at 2 meters from impact point
• Lethal Blast Radius: 2-3 meters (causes barotrauma)
• Blast Casualty Radius: 5-7 meters (stunning, disorientation)
• Crater Size: Approximately 0.3-0.5 meters diameter, 0.2-0.3 meters deep (in soil)

Fragmentation Characteristics

Fragment Production:

• Total Fragments: 300-500+ steel fragments (highly variable based on impact conditions)
• Fragment Weight Range: 1-15 grams per fragment (majority 2-5 grams)
• Fragment Shape: Irregular, jagged steel pieces

Fragment Velocity and Energy:

• Initial Velocity: ~1,200-1,500 m/s (3,900-4,900 fps) near detonation point
• Velocity at 10m: ~800-1,000 m/s (2,600-3,300 fps)
• Velocity at 30m: ~400-600 m/s (1,300-2,000 fps)
• Maximum Effective Range: 100-150 meters (fragments can travel this far)

Lethality Data:

• Kill Radius (5-7m): ~70-80% probability of incapacitation or death (personnel in open)
• Effective Casualty Radius (20-30m): ~30-40% probability of significant injury
• Fragment Penetration:
  • Soft tissue: Complete penetration within 50 meters
  • Soft body armor: May defeat at close range (<20m)
  • Hard body armor (ceramic/steel): Generally stops fragments
  • Light structures (wood): Penetrates at close to medium range

Fragment Pattern:

• Omnidirectional: Fragments disperse radially in all directions from impact point
• Ground Effect: Ground absorbs/deflects some fragments, creating uneven distribution
• Height Advantage: Impacts on hard surfaces or elevated positions improve fragment effectiveness
• Vegetation: Light vegetation (grass, brush) minimal effect on fragments; heavy trees provide some protection

Physical and Dimensional Specifications

Complete Round:

• Total Length: 255mm (10.04 inches)
• Maximum Diameter: 60mm (2.36 inches) – body and tail boom
• Fin Span (Deployed): ~100-120mm (4-4.7 inches)
• Total Weight: 1.41 kg (3.1 pounds / 49.9 ounces)

Component Breakdown:

High-Explosive Body:

• Length: 100-120mm (4-4.7 inches)
• Weight: ~800-900 grams (including explosive)
• Steel Thickness: 2-3mm
• Explosive Weight: 680 grams (1.5 lbs)

Fuze (M935):

• Length: ~30-40mm
• Weight: ~100 grams
• Threading: Standard 60mm mortar fuze threads

Tail Boom and Fin Assembly:

• Length: ~135mm (5.3 inches)
• Weight: ~300-350 grams (including propellant)
• Fin Count: 6 fins
• Propellant Weight: ~40-60 grams (base charge)

Ballistic Performance

Muzzle Velocity:

• Charge 0: ~100 m/s (328 fps) – minimum charge
• Charge 4: ~162 m/s (531 fps) – maximum charge (typical)
• Variable based on propellant increments

Maximum Range:

• Charge 4: 3,490 meters (3,815 yards / 2.17 miles)
• Charge 3: ~2,500-3,000 meters
• Charge 0: ~400-800 meters (minimum range)

Minimum Range:

• Practical: ~70-100 meters (safety minimum)
• Closer ranges risk fragments reaching crew

Time of Flight:

• Short Range (500m): ~10 seconds
• Medium Range (1500m): ~20 seconds
• Maximum Range (3490m): ~30-35 seconds

Trajectory:

• High-angle fire: Typical mortar trajectory (45-85 degrees elevation)
• Ballistic arc: Parabolic trajectory
• Terminal velocity: ~150-200 m/s at impact (depending on range/angle)

Accuracy:

• Probable Error (PE): ~30-50 meters at maximum range
• First-round hit probability: ~20-30% against point target at 2000m
• Adjusted fire: Trained crews achieve high accuracy with observation and adjustment

Environmental Specifications

Operating Temperature:

• Function Range: -40°F to +145°F (-40°C to +63°C)
• Storage Range: -60°F to +160°F (-51°C to +71°C)
• Optimal Performance: 32°F to 100°F (0°C to +38°C)

Temperature Effects on Ballistics:

• Hot propellant (+90°F / +32°C): Increased range (~5-10% increase)
• Cold propellant (-20°F / -29°C): Decreased range (~5-10% decrease)
• Range tables: Adjusted for temperature to maintain accuracy

Environmental Resistance:

• Humidity: Fuze and propellant moderately water-resistant
• Rain: Can be fired in rain (though accuracy may be affected)
• Immersion: Not waterproof; prolonged immersion degrades reliability
• Sand/Dust: Generally resistant; sealed components protected
• Salt Water/Corrosion: Steel body prone to corrosion over time

Altitude Effects:

• Function Altitude: Sea level to 15,000+ feet
• High Altitude: Reduced air density increases range slightly
• Fuze Function: Reliable at all altitudes within operating range

Propellant System

Primary Charge:

• Type: Smokeless powder (nitrocellulose-based)
• Weight: ~40-60 grams (base charge)
• Location: Tail boom assembly
• Ignition: Percussion primer in base

Augmenting Charges (Increments):

• Increments 1-4: Additional propellant charges attached to fins
• Function: Increase range progressively
• Removable: Crews can remove increments to decrease range
• Weight per Increment: ~5-10 grams

Propellant Performance:

• Burn Rate: Rapid deflagration (does not detonate)
• Gas Volume: Propels round to 162 m/s maximum velocity
• Pressure: ~40,000 psi in mortar tube (estimated)

Storage and Shelf Life

Storage Requirements:

• Temperature: -60°F to +160°F (-51°C to +71°C)
• Humidity: <70% relative humidity preferred
• Protection: Sealed containers with desiccant
• Orientation: Stored horizontally or vertically (no preference)

Shelf Life:

• Explosive: Indefinite when properly stored (Comp B highly stable)
• Propellant: 20+ years typical; inspection required periodically
• Fuze: 20+ years; mechanical components very durable
• Overall: Rounds properly stored remain functional for decades

Inspection Intervals:

• Visual Inspection: Annually for corrosion, damage
• Lot Testing: Every 5-10 years, statistical sampling for function testing
• X-ray Inspection: May be performed on aged lots

Indicators of Degradation:

• Heavy rust or corrosion on body
• Propellant discoloration or caking
• Fuze corrosion or damage
• Damaged fins or tail boom
• Such rounds withdrawn from service

Safety Data

Minimum Safe Distances:

For Mortar Crew:

• Firing Position: Behind mortar (backblast area clear to 10m)
• After Firing: Crew protected by terrain or remain in mortar pit
• Minimum Range: 70-100 meters (fragment safety for crew)

For Other Personnel:

• Immediate Area: 100 meters (from impact point)
• Casualty Area: 50-100 meters (fragment danger)
• Safe Area: 200+ meters (low probability of fragment injury)

Danger Zones:

• 0-7m from impact: Kill zone (high probability of death/incapacitation)
• 7-30m from impact: Casualty zone (significant injury likely)
• 30-100m from impact: Fragment danger (possible injury)
• 100m+ from impact: Minimal fragment danger

Cover Requirements:

• Hard Cover: Concrete, thick earthen berms (>1m), thick steel
• Soft Cover: Sandbags, wooden structures, light vehicles (marginal protection)
• Defilade: Low ground or trenches (protection from overhead fragments)

Comparative Data

M720 vs. Other Mortar Ammunition:

Characteristic	M720 (60mm)	M821 (81mm)	M933 (120mm)
Weight	1.41 kg	4.2 kg	13 kg
Explosive	680g Comp B	680g Comp B	2.1kg Comp B
Max Range	3,490m	5,650m	7,240m
Kill Radius	5-7m	10-15m	30-40m
Portability	High	Medium	Low (vehicle)
System Weight	21 kg	39 kg	145+ kg

M720 Advantages:

• Most portable indirect fire system
• Lightest ammunition for company-level support
• Rapid deployment – can be emplaced and firing within minutes
• Man-portable – entire system carried by 3-man crew

M720 Limitations Compared to Larger Mortars:

• Shorter range than 81mm/120mm
• Smaller casualty area (lighter explosive charge)
• Less effective against fortified positions
• Weather sensitivity – lighter round more affected by wind

Frequently Asked Questions

Q: How does the M720’s lethality compare to a hand grenade like the M67, and when would you use one over the other?

A: The M720 and M67 are both anti-personnel fragmentation weapons, but they serve different tactical roles with distinct lethality profiles. Lethality comparison: The M720 contains 680 grams of Composition B compared to the M67’s 180 grams—nearly four times more explosive—which translates to greater blast and fragmentation effects. The M720’s kill radius (5-7 meters) is similar to the M67’s (5 meters), but the M720’s casualty radius extends to 20-30 meters compared to 15 meters for the M67, meaning the mortar round affects a significantly larger area. The M720 produces 300-500+ fragments while the M67 produces 1,000+ smaller fragments, but the M720’s fragments come from a heavier steel body and may have greater individual mass and penetration capability. In raw destructive power, a single M720 is roughly equivalent to 3-4 M67 grenades detonating simultaneously. Tactical employment differences: Hand grenades are direct-fire weapons requiring line of sight to the target and limited by throwing range (30-40 meters), while the M720 is an indirect-fire weapon that can engage targets up to 3,490 meters away behind terrain features, buildings, or other obstacles. Grenades provide immediate response (seconds from decision to detonation), while mortars require setup and fire commands (1-3 minutes typically). Grenades are useful in close combat, room clearing, and situations where the enemy is within throwing range, while mortars engage targets beyond direct-fire range, suppress enemy positions during maneuvers, or provide sustained area fire. When to use each: Use M67 grenades for close-quarters battle (CQB), room clearing, immediate suppression of nearby enemies, defensive fighting positions, and when indirect fire assets are unavailable or inappropriate. Use M720 mortars for targets beyond direct-fire range, sustained suppression of enemy positions, engaging enemies in defilade (behind cover), coordinated fire support for maneuver elements, illumination or smoke missions, and when collateral damage can be minimized through precise indirect fire. In practice, infantry units carry both: grenades for immediate close-range threats and mortars for responsive indirect fire support. The M720’s range and indirect-fire capability make it far more versatile for supporting infantry maneuvers, while grenades excel in close combat where immediate, direct engagement is needed.

Q: What is the “arming distance” of the M720, and why is this safety feature critical for mortar crews?

A: The arming distance is the minimum distance the M720 must travel after being fired before its M935 fuze becomes armed and capable of detonating. For the M720, this arming distance is approximately 5-25 meters from the muzzle, depending on specific conditions. This safety feature is absolutely critical because it creates a safety bubble around the mortar position where the round cannot detonate even if something goes catastrophically wrong. Here’s why it matters: During firing, there are several potential malfunctions that could cause the round to impact very close to the crew: (1) Squib load – weak propellant burn causing the round to barely clear the tube and land nearby, (2) Tube obstruction – debris or a previous dud in the tube causing the round to exit at low velocity, (3) Damaged round – a compromised tail assembly might cause erratic flight and immediate impact near the position, or (4) Hang fire followed by drop – if a round fails to fire initially and is removed from the tube, it might ignite when dropped. The arming distance ensures that in any of these scenarios, the round will not detonate because the fuze hasn’t armed yet. How arming works: The M935 fuze requires both setback force (from launch acceleration) AND centrifugal force (from spin during flight) to arm. During the first 5-25 meters of flight, one or both of these safeties is still engaged, mechanically blocking the striker from reaching the detonator. Only after the round has traveled beyond the arming distance and experienced both high-G acceleration and sufficient spin do the mechanical safeties release, allowing the striker to function on impact. Practical implications: This means if you drop an M720 round in the mortar pit, it cannot detonate—the fuze is completely safe without firing acceleration and spin. If a squib occurs and the round lands 10 meters away, it will not detonate because the fuze hasn’t completed its arming sequence. Mortar crews can operate with confidence knowing that malfunctions within the arming distance will not result in detonation. This safety feature has undoubtedly saved countless lives over decades of mortar operations. Contrast with hand grenades: Unlike the M67 grenade which arms immediately when the safety lever releases (fuze burning starts instantly), the M720’s arming is velocity and distance-dependent, providing far greater safety for the crew. The trade-off is that if you need a very close-range engagement (say, 50 meters), the round will function normally since it arms well before impact, but the crew must be in protected positions due to the casualty radius extending back toward the firing point.

Q: Can M720 mortar rounds be fired in a “handheld” mode without a baseplate and bipod, and how does this affect accuracy and safety?

A: Yes, the M224 60mm mortar system (which fires the M720) is specifically designed to operate in handheld mode as well as conventional emplaced mode, making it unique among mortar systems. This capability is a key feature that distinguishes the M224 from larger mortars. Handheld firing mode: In handheld mode, one crew member shoulders the mortar tube (which has a special shoulder stock), another crew member drops the M720 round down the tube, and the round fires immediately upon hitting the firing pin at the base. There is no baseplate or bipod—the soldier absorbs the recoil directly. This mode allows extremely rapid employment (literally seconds from decision to fire the first round) and is used when the tactical situation requires immediate suppressive fire without time to emplace the mortar properly. Safety considerations: Handheld firing is generally safe when proper procedures are followed: (1) The operator must maintain proper stance and body positioning to absorb recoil safely (typically kneeling or standing with good balance), (2) The barrel must be pointed in a safe direction (downrange, elevated at proper angle), (3) All personnel must be clear of the muzzle and backblast area (5-10 meters behind tube), (4) Minimum range restrictions apply—generally don’t fire handheld at targets closer than 100-150 meters to ensure crew is outside casualty radius, and (5) The operator must brace properly or risk injury from recoil (dislocated shoulder, facial injuries if tube strikes face). Accuracy limitations: Handheld firing significantly degrades accuracy compared to emplaced firing with bipod and baseplate. In handheld mode, accuracy depends entirely on the operator’s ability to judge angle and direction—there are no aiming mechanisms, range adjustments, or precise elevation controls. Typical accuracy in handheld mode might be 100-200 meter dispersion at 1,000 meters compared to 30-50 meters with properly emplaced mortar. This makes handheld firing suitable for area suppression (general area where enemy is located) but not for precision engagement of specific targets. Tactical applications: Handheld mode is used for: (1) Immediate suppression when ambushed or in contact—fire several rounds quickly toward enemy to disrupt attack, (2) Emergency illumination – rapidly deploy illumination rounds when caught in darkness, (3) Smoke screening – quickly lay smoke between friendly forces and enemy, (4) Hasty fire support when there’s no time to properly emplace the mortar. Transition to conventional mode: Once the immediate threat is suppressed, crews typically transition to conventional emplaced mode with baseplate and bipod for sustained, accurate fire. The handheld capability provides a critical bridge between immediate need and deliberate indirect fire support. Important limitations: (1) Sustained handheld firing is physically exhausting and risks injury, (2) Accuracy is too poor for danger-close missions near friendly forces, (3) Maximum range may be slightly reduced due to suboptimal firing angles, and (4) Fire-for-effect missions require emplaced mode for proper accuracy. The handheld capability reflects the M224/M720 system’s design philosophy: provide infantry with the most responsive, portable indirect fire system possible, accepting some limitations in exchange for unmatched tactical flexibility.

Q: What happens if a mortar crew needs to stop firing but there’s already a round loaded in the tube that hasn’t fired (a “misfire”), and how dangerous is this situation?

A: A misfire—when an M720 round is loaded into the M224 mortar tube but fails to fire—is one of the most dangerous situations mortar crews face and requires strict adherence to safety procedures. What causes misfires: Misfires typically occur due to: (1) Faulty percussion primer in the round’s tail boom—the primer fails to ignite when struck by the mortar’s firing pin, (2) Damaged firing pin in the mortar base—worn or broken pin doesn’t strike primer with sufficient force, (3) Obstruction or debris preventing proper contact between primer and firing pin, or (4) Defective propellant—primer ignites but propellant fails to burn (very rare). The danger: A misfired round is exceptionally dangerous because you now have a live explosive device with a percussion-initiated propellant charge sitting in the mortar tube, and you don’t know why it didn’t fire. The most dangerous scenario is a hang fire—a delayed ignition where the primer or propellant ignites seconds or minutes after the initial attempt. If a crew member removes the round from the tube during a hang fire, it could ignite in their hands or at their feet, causing catastrophic injuries or death. Even if it’s not a hang fire, the round might fire unexpectedly if disturbed, dropped, or jostled. Proper misfire procedures (critical): If a round is dropped down the tube and fails to fire: (1) Immediately announce “MISFIRE!” to alert all crew members, (2) Maintain firing position—do not approach the mortar, (3) Wait minimum 60 seconds (many military SOPs require 90 seconds or more)—this waiting period allows any hang fire to complete before approaching, (4) After waiting period, carefully approach the mortar from the side (never from muzzle or base), (5) Inspect the round in the tube—look for obvious problems (round not fully seated, visible damage), (6) If safe, attempt second firing—re-cock firing mechanism (if applicable) and drop another round (the second round’s impact may fire the first round), and (7) If second attempt fails, carefully remove round—lift mortar tube to horizontal, allow round to slide out into crew member’s hands (never let it drop), then gently place round on ground away from firing position. After removal: Misfired rounds must be segregated, marked, and turned in to EOD or ammunition supply for inspection and proper disposal. Never attempt to fire a misfired round again—there may be a defect that makes it unsafe. Some units require misfired rounds to be left in place and EOD called for safe removal rather than allowing crew to handle them. Hang fire scenario: If a hang fire occurs and the round ignites while being handled or just after removal, the result is usually catastrophic for the crew member handling it—propellant ignition at face/chest level with subsequent muzzle blast and potentially the round detonating immediately after exiting the tube in the mortar pit. This is why the 60-90 second wait is absolutely non-negotiable. Prevention: Regular inspection and maintenance of the mortar firing mechanism, careful inspection of ammunition before loading (check for damaged primers, corrosion, or obvious defects), and proper training are the best defenses against misfires. Crews must never become complacent—even though misfires are relatively rare (~1-3% of rounds), they will eventually occur, and when they do, following proper procedures is the only thing between the crew and potential tragedy. The U.S. military’s misfire procedures have been refined over decades of experience and have saved countless lives by preventing hang fire accidents.

Q: How does weather (temperature, humidity, wind, altitude) affect M720 mortar accuracy and what adjustments do crews make?

A: Weather has significant effects on M720 mortar ballistics, and trained crews must make careful adjustments to maintain accuracy, especially at longer ranges. Understanding these effects is critical for effective indirect fire support. Temperature effects (most significant): Temperature affects both the propellant burn rate and air density. Hot propellant burns faster and more completely, generating more gas pressure and higher muzzle velocity, which translates to increased range (5-10% increase at 100°F vs. 60°F standard). Cold propellant burns slower and less completely, reducing muzzle velocity and decreasing range (5-10% decrease at 0°F vs. 60°F). This effect compounds over longer ranges—at 3,000 meters, temperature variations can cause 150-300 meter range changes. Crews compensate by using range tables that include temperature corrections. Before a mission, crews measure ambient temperature and apply corrections to elevation settings. For example, if firing in 90°F heat, the crew might reduce elevation by 1-2 degrees compared to standard conditions to avoid overshooting the target. Modern digital fire control systems automatically calculate these corrections. Humidity effects (moderate): High humidity increases air density slightly, creating more drag on the round and reducing range marginally (usually <2-3% effect). Moisture can also affect propellant if rounds have been exposed to rain or high humidity for extended periods—wet propellant may burn less reliably. However, humidity effects are generally small compared to temperature and are often ignored for tactical fire missions unless extreme. Wind effects (significant at range): Crosswinds deflect the relatively light M720 round during its 10-30 second flight time, causing left/right deviation from the intended target. A 10 mph crosswind can cause 20-50 meter deflection at maximum range. Crews use wind speed and direction measurements (observed with wind meters or estimated by flag movement, vegetation, etc.) to calculate deflection corrections. The fire direction center applies wind corrections to the azimuth (left/right aiming) setting. Strong headwinds reduce range (similar to increased air density), while tailwinds increase range. Gusty or variable winds are particularly problematic because they create unpredictable deflections—in these conditions, crews may need to fire several adjustment rounds before achieving accuracy. Altitude effects (moderate): Higher altitude means lower air density, which reduces drag on the round and increases range slightly (3-5% increase at 5,000 feet vs. sea level). Crews operating in mountainous terrain must account for altitude when using range tables. Additionally, high-altitude environments often have thinner, colder air which compounds range effects. Some range tables include altitude corrections; modern fire control computers handle this automatically. Barometric pressure (related to altitude and weather): Low pressure systems (storms, low-altitude dense air) increase drag and reduce range. High pressure systems have the opposite effect. While these effects exist, they’re usually small enough that they’re incorporated into general weather corrections rather than calculated separately. Combined effects example: Imagine firing a mission at 3,000 meters range on a cold (30°F), windy (15 mph crosswind), high-altitude (7,000 feet) day. Cold temperature reduces range significantly (maybe -200 meters), high altitude increases range slightly (+100 meters), and crosswind deflects the round right (maybe 40 meters at impact). The crew must apply corrections for all three: increase elevation to compensate for cold temperature effect, reduce elevation slightly for altitude, and adjust azimuth left to counter the crosswind. Without these corrections, the first round might land 100+ meters from the intended target—potentially ineffective or dangerous to friendlies. Practical fire direction: In practice, crews measure weather conditions before and during fire missions using: (1) Thermometers for air and propellant temperature, (2) Wind meters or observation for wind speed/direction, (3) Altimeters or maps for altitude, (4) Barometers for atmospheric pressure (if available). This data feeds into firing tables (printed charts) or digital fire control systems (computers) that calculate exact elevation and deflection settings for each target. Modern systems make these calculations instantly; traditional methods require manual chart reading and calculation. Adjustment fire: Because weather effects are complex and conditions change, mortar crews typically fire adjustment rounds to “walk” fire onto target. The forward observer watches the impact and calls corrections (“add 50 meters,” “left 20 meters”), allowing the crew to compensate for any weather effects not perfectly calculated. Once accurate, the crew fires fire-for-effect (multiple rounds on target). Bottom line: Weather significantly affects mortar accuracy, especially at longer ranges. Professional mortar crews are trained to measure, calculate, and apply weather corrections as a standard part of every fire mission. Failure to account for weather can result in mission failure or, worse, friendly fire casualties from rounds landing in the wrong place.

Q: What are the legal and ethical considerations surrounding the use of mortars like the M720 in modern urban warfare?

A: The use of indirect fire weapons like the M720 in urban environments involves complex legal, ethical, and tactical considerations under international law, particularly the Law of Armed Conflict (LOAC) and Rules of Engagement (ROE). These considerations have become increasingly important in modern conflicts where combat occurs in densely populated areas. Legal framework (International Humanitarian Law): Use of mortars must comply with the Geneva Conventions and their Additional Protocols, which establish core principles: (1) Distinction – combatants must distinguish between military objectives and civilians/civilian objects; indiscriminate attacks are prohibited, (2) Proportionality – anticipated military advantage must not be outweighed by expected civilian harm, (3) Precautions – all feasible precautions must be taken to minimize civilian casualties and damage, and (4) Military necessity – force used must be necessary to achieve a legitimate military objective. Challenges with mortars in urban areas: The M720’s characteristics create specific challenges: (1) Area weapon – the 20-30 meter casualty radius means the weapon affects a large area, making it difficult to limit effects to only military targets in dense urban terrain where combatants and civilians are intermixed, (2) Indirect fire – crews cannot see the target directly, relying on forward observers or target coordinates; this increases risk of errors in target identification or location, (3) Collateral damage – fragments and blast easily penetrate civilian structures, creating risk of casualties in adjacent buildings, and (4) Accuracy limitations – even with modern fire control, 30-50 meter probable error at range means some rounds will miss the intended target. Rules of Engagement (ROE) restrictions: Modern ROE typically impose strict limitations on mortar use in urban areas: (1) Positive identification (PID) of enemy forces may be required before engaging, (2) Proximity restrictions – may prohibit fires within certain distances of known civilian concentrations, (3) Approval authorities – higher command levels may need to approve fire missions in urban areas, (4) Proportionality assessment – commander must weigh expected civilian harm against military advantage, and (5) Mitigation measures – requirement to use smallest munition necessary, precise targeting, warning civilians if feasible. Ethical considerations: Beyond legal requirements, commanders face ethical questions: Is the military objective important enough to justify the risk to civilians? Could the objective be achieved with less destructive means (direct fire, infantry assault, precision-guided munitions)? Are there known or suspected civilians in the target area? How certain is the target intelligence? What are the second-order effects (damage to infrastructure, displacement of civilians, propaganda value to the enemy)? Practical examples from recent conflicts: Iraq/Afghanistan experience: U.S. forces faced intense scrutiny over indirect fire use in populated areas. High-profile incidents where mortar or artillery rounds killed civilians led to: (1) Increasingly restrictive ROE, (2) Requirements for multiple confirmation sources before engaging, (3) Use of smaller munitions (60mm preferred over 81mm/120mm in many situations), (4) Integration of precision-guided munitions where available, and (5) Extensive investigations after any civilian casualty incident. Tactical adaptations: To balance effectiveness with legal/ethical requirements, modern forces have developed practices including: (1) Precision targeting – extensive reconnaissance and intelligence before engaging, (2) Observer control – forward observers with eyes on target confirm military nature of target, (3) Minimized danger area – using smallest effective munition (M720 60mm rather than larger mortars when adequate), (4) Restricted engagement zones – designating no-fire areas around schools, hospitals, mosques, dense residential areas, (5) Warning procedures – when tactically feasible, warning civilians to evacuate (though this may also warn enemy), and (6) After-action review – investigating every mission for compliance and potential civilian harm. Tension between military effectiveness and civilian protection: Combat in urban areas creates inherent tension: Mortar fire support saves friendly lives by suppressing enemy positions, but the same fires risk civilian casualties. Overly restrictive ROE may prevent effective use of mortars, potentially increasing friendly casualties and prolonging conflict. Too permissive ROE may result in civilian casualties that violate law, harm moral standing, and aid enemy propaganda. Commanders must constantly balance these competing concerns. The M720’s role in this context: The 60mm mortar’s relatively small warhead and casualty radius make it preferred over larger mortars in urban environments when indirect fire is necessary—it provides the minimum destructive force needed, reducing (though not eliminating) civilian harm. However, it’s not a precision weapon, and all the legal/ethical considerations still apply. Modern trends: Increasing emphasis on precision-guided munitions (GPS-guided mortar rounds, drone strikes, precision artillery) aims to reduce collateral damage while maintaining fire support capability. However, these systems are expensive and not always available, meaning conventional mortars like the M720 will remain relevant, requiring continued emphasis on lawful and ethical employment. Bottom line: Using M720 mortars in urban warfare is legally permissible under international law when employed with proper precautions, discrimination, and proportionality. However, it requires exceptional discipline, rigorous target verification, constant consideration of civilian harm, and willingness to accept risk to friendly forces to protect civilians. Professional militaries invest heavily in training, systems, and procedures to ensure indirect fire weapons are used lawfully and ethically, recognizing that failure to do so not only violates law but undermines strategic objectives and moral legitimacy.

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Safety Notice

⚠️ WARNING: All information provided is for educational and identification purposes only.

• Never approach, handle, or attempt to move any suspected ordnance, including M720 mortar rounds
• All unexploded ordnance (UXO) and dud mortar rounds must be treated as armed and extremely dangerous
• Suspected ordnance should be reported immediately to military authorities, law enforcement, or explosive ordnance disposal (EOD) teams
• Do not attempt to defuse, disarm, or recover military ordnance without proper training and authorization
• This lesson is intended for military training, EOD education, and historical/technical understanding—not for unauthorized ordnance handling

If you discover a suspected M720 mortar round or similar ordnance:

1. Do not touch or move the item
2. Evacuate the immediate area (minimum 100 meters)
3. Mark the location from a safe distance
4. Report to authorities immediately (police, military, EOD)
5. Establish a cordon to prevent others from approaching
6. Never assume an old, damaged, or partially buried round is “safe”

Specific warnings for M720 rounds:

• Dud mortar rounds are FULLY ARMED—the fuze armed during flight even though detonation failed
• The explosive filling (Composition B) remains potent indefinitely
• Impact-damaged rounds may be MORE sensitive than normal
• Corrosion may make fuzes unstable and unpredictable
• Never attempt to unscrew the fuze or disassemble any part of the round
• Mortar rounds found on ranges, battlefields, or civilian property must be handled only by EOD professionals

Legal warnings:

• Possession of live military ordnance is illegal in most jurisdictions
• Unauthorized ordnance handling can result in criminal charges
• Even “demilitarized” or “training” ordnance may contain explosive components