US M720 60mm HE Mortar

1. Overview

The M720 is a United States 60mm high-explosive (HE) mortar cartridge specifically designed for the M224 Lightweight Company Mortar System (LWCMS). Introduced in the mid-1980s, the M720 represented a significant advancement in 60mm mortar ammunition, offering extended range and the revolutionary M734 Multi-Option Fuze that provides unprecedented tactical flexibility with proximity, near-surface burst, impact, and delay settings.

Note: The M720 is a high-explosive round, not an illumination round. The 60mm illumination cartridge is the M721. This lesson covers the M720 HE cartridge.

The M720, along with its insensitive munitions-compliant successor the M720A1, serves as the primary HE round for US infantry company-level mortar sections.

2. Country/Bloc of Origin

  • Country: United States of America
  • Development Period: 1970s–1980s
  • Type Classification Date: January 1986
  • Manufacturers: American Ordnance LLC (Iowa and Milan Army Ammunition Plants) and other contractors
  • Service Entry: Mid-1980s with M224 LWCMS fielding

3. Ordnance Class

  • Type: Mortar Cartridge, High-Explosive (HE)
  • Primary Role: Anti-personnel and light materiel engagement through fragmentation and blast effects
  • Delivery Method: Muzzle-loaded, fin-stabilized mortar projectile
  • Classification: Standard A ammunition for M224 LWCMS

4. Ordnance Family / Nomenclature

  • Official Designation: Cartridge, 60mm HE, M720
  • Related Variants:
    • M720A1: Insensitive munitions (IM) compliant version with PAX-21 explosive fill and M734A1 fuze
    • M720A2: Further IM improvements
    • M768: Point-detonating variant with M783 PD fuze (lower cost training alternative)
    • M888: Point-detonating variant with M935 PD fuze
  • Compatible Weapon Systems:
    • M224 60mm Lightweight Company Mortar System (primary)
    • M224A1 60mm Mortar (improved version)
    • M19 60mm Mortar (at reduced charges: maximum charge 2 for training, charge 3 in combat)
  • Unit Cost: Approximately $497 (FY2005)

5. Hazards

Primary Hazards

  • Blast: High-explosive detonation produces significant overpressure
  • Fragmentation: High-fragmentation steel body produces numerous lethal fragments
  • Effective Casualty Radius: Approximately 20–30 meters
  • Lethal Radius: Approximately 10–15 meters

Multi-Option Fuze Hazards

  • Proximity Setting: Electronic fuze with radar emitter; round detonates 1–4 meters above ground
  • Near-Surface Burst: Detonates 0–1 meter above target
  • Impact: Functions on ground contact
  • Delay: Functions 0.5 seconds after impact (allows penetration)

UXO Considerations

  • Dud Rate: Multi-option fuze includes backup modes; if proximity fails, automatically attempts near-surface burst, then impact, then delay
  • Electronic Fuze: Battery-powered electronic components may remain active in unexploded rounds
  • Fuze Complexity: The M734’s sophisticated electronics create additional unpredictability in UXO scenarios

Special Hazards

  • Proximity-fuzed rounds that fail to detonate remain extremely dangerous
  • Electronic fuzes may be sensitive to electromagnetic interference
  • The M720A1’s PAX-21 insensitive explosive is designed to resist unintended detonation but remains lethal when properly initiated

6. Key Identification Features

Dimensions

  • Caliber: 60mm
  • Overall Length: Approximately 381mm (15 inches)
  • Body Diameter: 60mm nominal
  • Complete Round Weight: Approximately 1.68 kg (3.7 lbs)
  • Explosive Filler Weight: Approximately 0.3 kg (0.66 lbs)

Physical Characteristics

  • Body Construction: High-fragmentation alloy steel
  • Body Shape: Streamlined ogive configuration, longer than legacy M49 series
  • Fin Assembly: Six-blade fin assembly with obturating ring
  • Fuze: Large, distinctive M734 multi-option fuze with external setting dial

Color and Markings

  • Body Color: Olive drab (OD green)
  • Marking Color: Yellow stenciling indicating HE content
  • Typical Markings:
    • “60MM M720” or “60MM M720A1” (designation)
    • Lot number and date
    • Manufacturer code
    • Explosive fill type

Distinctive Features

  • M734 Fuze: Large cylindrical fuze body with visible setting dial marked PRX/NSB/IMP/DLY
  • Extended Length: Noticeably longer than legacy M49 series rounds
  • Modern Construction: Clean machining and finish characteristic of modern production
  • Obturating Ring: Delrin (plastic) ring on body for bore sealing

7. Fuzing Mechanisms

Primary Fuze: M734 Multi-Option Fuze

The M734 represents a revolutionary advancement in mortar fuze technology, providing four selectable function modes in a single fuze.

Fuze Settings

  1. Proximity (PRX): Radar-activated airburst at 1–4 meters above target
    • Maximizes fragment dispersion against personnel in the open
    • If PRX fails, automatically defaults to NSB
  2. Near-Surface Burst (NSB): Detonates at 0–1 meter above target
    • Effective against personnel in fighting positions
    • If NSB fails, automatically defaults to IMP
  3. Impact (IMP): Detonates on ground contact
    • Standard point-detonating function
    • If IMP fails, automatically defaults to DLY
  4. Delay (DLY): Detonates 0.5 seconds after impact
    • Allows penetration of light cover before detonation
    • Effective against bunkers and structures

Fuze Operation

  • Setting: Rotary dial on fuze body; no tools required; can be changed multiple times before firing
  • Power: Internal battery activated during launch
  • Arming: Setback and spin-activated arming sequence
  • No Safety Pins/Wires: Designed for rapid preparation without removal of safety devices

Backup Cascade

The M734’s backup cascade ensures high probability of function:

  • PRX → NSB → IMP → DLY

M734A1 (for M720A1)

The M734A1 fuze used with the M720A1 incorporates improved reliability and countermeasure resistance while maintaining the same operational modes.

8. History of Development and Use

Development Background

The M720 was developed as part of the M224 Lightweight Company Mortar System program to provide US infantry with improved company-level indirect fire capability. The legacy M2 and M19 mortars with M49-series ammunition were limited to approximately 2,000 meters maximum range. The M224/M720 combination extended this to nearly 3,500 meters while introducing the game-changing multi-option fuze.

Key Milestones

  • Mid-1970s: M224 LWCMS development begins
  • January 1986: M720 type classified
  • Late 1980s: Fielding to US Army and Marine Corps units
  • November 2001: M720A1 type classified (IM compliant)
  • September 2004: M720A1 material release

Combat Employment

  • Operation Desert Storm (1991): First major combat use
  • Somalia (1992–1993): Urban combat employment
  • War in Afghanistan (2001–2021): Extensive use in mountainous terrain
  • Iraq War (2003–2011): Urban and rural operations
  • Global War on Terror: Continued employment worldwide

Tactical Revolution

The M734 multi-option fuze transformed 60mm mortar employment:

  • Proximity burst: Dramatically increased effectiveness against personnel in the open
  • Near-surface burst: Improved effects against troops in fighting positions
  • Selectable modes: Single ammunition type replaced need for multiple fuze types
  • No safety devices: Reduced preparation time for rapid fire missions

Current Status

  • In active service with US Army and Marine Corps
  • M720A1 is preferred warfighting round due to IM compliance
  • M768 (PD variant) used primarily for training due to lower cost
  • Exported to numerous allied nations

9. Technical Specifications

SpecificationValue
Caliber60mm
Overall Length~381mm (15 in)
Body Diameter60mm
Complete Round Weight~1.68 kg (3.7 lbs)
Explosive Fill (M720)Composition B or TNT
Explosive Fill (M720A1)PAX-21 (IM compliant)
Filler Weight~0.3 kg (0.66 lbs)
Fuze (M720)Multi-Option, M734
Fuze (M720A1)Multi-Option, M734A1
PropellantM204 (4 increments)
Maximum Range3,490 m (3,816 yds)
Minimum Range70 m
Rate of Fire (Max)30 rounds/min
Rate of Fire (Sustained)15 rounds/min
Unit Cost (M720A1)~$489 (FY2005)

10. Frequently Asked Questions

Q: What makes the M720 superior to the legacy M49 series? A: The M720 offers three major advantages: (1) Extended range of 3,490 meters versus approximately 2,000 meters for M49 series; (2) The M734 multi-option fuze providing proximity, near-surface burst, impact, and delay modes in one round; and (3) Improved high-fragmentation steel body for enhanced lethality. These improvements dramatically increased the tactical utility of company-level mortar sections.

Q: How does the proximity fuze setting work? A: The M734 fuze contains a small radar transmitter/receiver. When set to proximity mode, the fuze emits radar signals during terminal descent. When the radar detects the ground at 1–4 meters distance, it initiates detonation. This airburst maximizes fragment dispersion against personnel in the open, who receive fragments from above rather than just laterally.

Q: What is the difference between M720 and M720A1? A: The M720A1 is an insensitive munitions (IM) compliant version. Key differences: (1) PAX-21 insensitive explosive fill replaces Composition B; (2) Modified fuze adapter and packaging; (3) M734A1 fuze with improved reliability and countermeasure resistance; (4) High-fragmentation steel (HF-1) body maintains lethality despite insensitive fill. The M720A1 is the preferred combat round.

Q: Can the M720 be fired from legacy M2 or M19 mortars? A: The M720 can be fired from the M19 mortar at reduced charges only (maximum charge 2 for training, charge 3 in combat emergency). It is not recommended for use in the M2 mortar. The M720 was specifically designed for the M224’s longer barrel and achieves optimal performance only in that system.

Q: What happens if the M734 fuze malfunctions? A: The M734 incorporates a backup cascade system. If proximity mode fails to function, the fuze automatically attempts near-surface burst. If that fails, it attempts impact detonation. If impact fails, it defaults to delay mode (0.5 seconds after impact). This cascade maximizes probability of function while maintaining tactical utility even in degraded conditions.

Q: Why is the M720A1 preferred over the M720 for combat? A: The M720A1’s insensitive munitions compliance means it is significantly more resistant to unintended detonation from fire, bullet impact, or sympathetic detonation. This improves safety for soldiers handling and transporting the ammunition in combat conditions. The IM features also reduce logistics risks. Lethality is maintained through the high-fragmentation steel body.

Q: What are the maximum charges for handheld firing of the M224? A: When firing the M224 in handheld mode (without bipod/baseplate), the M720 and M888 cartridges are limited to charge 1 maximum. Higher charges generate excessive recoil for handheld control and risk injury to the gunner.

Safety Notice

⚠️ All ordnance should be considered dangerous until verified safe by qualified EOD personnel.

This information is for educational and identification purposes only

Never handle, move, or disturb suspected UXO

M734 proximity fuzes in unexploded rounds are particularly dangerous due to electronic components

Establish a safe perimeter and mark the location

Report findings to military or law enforcement authorities immediately