US 105mm M1 Bursting Smoke Projectile

Overview

The 105mm M1 Bursting Smoke Projectile is a World War II-era artillery round designed to produce an instantaneous smoke screen through the detonation of a bursting charge that disperses white phosphorus (WP) or hexachloroethane (HC) smoke mixture. Unlike base-ejection smoke rounds that release canisters, the M1 creates an immediate smoke cloud upon impact, making it valuable for rapid obscuration of enemy positions, marking targets, or providing emergency screening for friendly forces. The projectile remains significant in ordnance education due to its widespread historical use and the continued presence of unfired or partially functioning rounds in former conflict areas.

• Country: United States of America
• Development Period: Late 1930s to early 1940s
• Service Introduction: Entered service prior to and during World War II
• Production: Manufactured by multiple U.S. arsenals and contractors throughout WWII and the Korean War era
• International Use: Supplied to Allied nations during WWII and subsequently to numerous U.S. allies through military assistance programs

Ordnance Class

• Type: Artillery projectile (howitzer ammunition)
• Primary Role: Smoke screening, target marking, incendiary effect (secondary)
• Delivery Method: Fired from 105mm howitzers (M2A1, M101, M102, and related systems)
• Category: Bursting-type smoke munition

Ordnance Family/Nomenclature

Official Designations

• M1 Smoke (WP) – White phosphorus fill
• M1 Smoke (HC) – Hexachloroethane smoke mixture fill

Related Variants

• M60 Smoke (WP) – Later improved design with similar function
• M84 Smoke (HC) – Base-ejection smoke round (different operating principle)
• M314 Illumination – Uses similar projectile body design for illumination role
• M1 HE – High explosive variant sharing the same basic projectile configuration

NATO Terminology

• Classified under smoke/screening munitions for 105mm howitzer systems

Common Names

• “Willie Pete” (slang for white phosphorus variant)
• “Willy Peter”
• “Bursting smoke”

Hazards

Primary Hazard Types

• Thermal/Incendiary: White phosphorus burns at approximately 815°C (1,500°F) and will ignite combustible materials on contact
• Chemical Burn: WP causes severe chemical burns to skin and tissue; particles continue burning until oxygen supply is cut off or phosphorus is consumed
• Toxic Fume Inhalation: WP combustion produces phosphorus pentoxide fumes that are highly toxic when inhaled
• Fragmentation: The steel projectile body produces fragmentation upon detonation
• Blast: Bursting charge creates localized blast effects

Sensitivity Considerations

• Unfired rounds are relatively stable when properly stored
• Fuzes may become increasingly sensitive with age and environmental degradation
• WP fill becomes more hazardous if projectile body is compromised (spontaneous ignition in air)
• Corroded or damaged projectiles present elevated handling risks

Environmental Factors

• Heat can increase internal pressure and sensitivity
• Physical damage to projectile body may expose WP fill to air, causing spontaneous ignition
• Water does not extinguish WP—it burns underwater and reignites when exposed to air

UXO Considerations

• Unexploded M1 smoke rounds may have partial fuze function, leaving WP fill intact
• Dud rounds present both explosive and chemical hazards
• Aged WP may form more sensitive compounds
• Kill Radius: Fragmentation danger extends approximately 35 meters; thermal/chemical effects concentrated at point of impact with smoke dispersal dependent on wind conditions

Special Hazards

• WP particles can embed in clothing and skin, continuing to burn
• Secondary fires from WP ignition of surrounding materials
• Smoke can cause respiratory distress even without direct WP contact

Key Identification Features

Dimensions

• Length: Approximately 494mm (19.4 inches) including fuze
• Diameter: 105mm (4.13 inches)
• Weight: Approximately 14.5 kg (32 lbs) complete with fuze

Shape and Profile

• Ogival (curved) nose section
• Cylindrical body with rotating band near base
• Boat-tailed base (tapered)

Color Scheme and Markings

• Body Color: Light green (older rounds) or olive drab
• Markings: Yellow band around body indicates smoke/screening agent
• Stenciled Text: “SMOKE WP” or “SMOKE HC” typically stenciled in yellow
• Lot Numbers: Manufacturing lot and date information stenciled on body
• Fuze Marking: Fuze well area may indicate compatible fuze types

Distinctive Features

• Single yellow band distinguishes smoke rounds from HE (no band or single yellow band) and illumination rounds (white markings)
• Threaded fuze well at nose
• Rotating band (copper or gilding metal) near base for engaging rifling
• Bursting charge cavity visible in sectioned training aids

Material Composition

• Body: Forged or drawn steel
• Rotating Band: Copper or gilding metal alloy
• Fill: White phosphorus (WP) or hexachloroethane mixture (HC)
• Bursting Charge: TNT or Composition B

Fuzing Mechanisms

Compatible Fuzes

• M51 Point-Detonating Fuze – Most common; superquick or delay settings
• M48 Point-Detonating Fuze – Superquick action
• M557 Point-Detonating Fuze – Later production; superquick/delay options

Arming Sequence

1. Bore Safety: Fuze remains unarmed until projectile exits the gun tube
2. Setback Arming: Acceleration forces during firing initiate arming sequence
3. Centrifugal Arming: Spin imparted by rifling completes arming process
4. Armed State: Fuze becomes fully armed after traveling a safe distance from the gun (typically 20-40 meters)

Detonation

• Superquick (SQ): Detonates on contact with target
• Delay: Brief delay (0.05 seconds) allows slight penetration before detonation

Safety Features

• Interrupter mechanism prevents detonation until spin-armed
• Bore safety ensures round cannot detonate in the gun tube
• Transport safety (varies by fuze type)

Functioning

1. Impact with target crushes firing pin mechanism
2. Firing pin strikes detonator
3. Detonator initiates booster charge
4. Booster detonates main bursting charge
5. Bursting charge ruptures projectile body and disperses WP/HC fill

History of Development and Use

Development Background

The M1 Bursting Smoke Projectile was developed in the late 1930s as the U.S. Army modernized its artillery capabilities. The 105mm howitzer was becoming the standard divisional artillery piece, and effective smoke munitions were essential for maneuver warfare doctrine. The bursting smoke design was chosen for its ability to produce immediate smoke effects, unlike slower-acting base-ejection rounds.

World War II Service

The M1 saw extensive use across all theaters of World War II:

• European Theater: Used for screening river crossings, concealing troop movements, and marking targets for air support
• Pacific Theater: Employed in island-hopping campaigns, often used for its incendiary secondary effects against fortified positions
• North African Campaign: Critical for desert warfare obscuration

Korean War

The projectile continued in service during the Korean War (1950-1953), where mountainous terrain made smoke screening particularly valuable for concealing movements and withdrawals.

Post-War Evolution

• Gradually supplemented by improved designs (M60 series)
• Remained in reserve stocks and was supplied to allied nations through Military Assistance Programs
• Eventually declared obsolete in front-line U.S. service but remained in some allied inventories into the 1970s-1980s

Current Status

• Obsolete in active U.S. service
• UXO from WWII and Korean War continues to be encountered in former conflict areas
• Training and inert examples used for EOD education
• Some allied nations may retain stocks in reserve

Production Figures

Millions of rounds were produced during WWII, exact figures vary by variant and manufacturing period.

Technical Specifications

Specification	Detail
Caliber	105mm
Overall Length	~494mm (19.4 in) with fuze
Projectile Weight	~14.5 kg (32 lbs) complete
Fill Weight (WP)	~1.8 kg (4 lbs) white phosphorus
Fill Weight (HC)	~2.0 kg (4.4 lbs) HC smoke mixture
Bursting Charge	~0.4 kg (0.9 lbs) TNT or Comp B
Muzzle Velocity	472 m/s (1,550 ft/s) typical
Maximum Range	~11,200 m (12,250 yds)
Smoke Duration	1-2 minutes (WP); longer for HC
Operating Temperature	-40°C to +52°C (-40°F to +125°F)

Smoke Characteristics

• WP: Produces dense white smoke immediately; burning particles create persistent smoke as long as phosphorus remains
• HC: Grayish-white smoke; less incendiary effect than WP

Frequently Asked Questions

Q: What is the primary difference between the M1 WP and M1 HC smoke projectiles? A: The M1 WP (white phosphorus) contains phosphorus that burns intensely upon exposure to air, producing a dense white smoke and significant incendiary effects. The M1 HC (hexachloroethane) contains a chemical smoke mixture that produces smoke through a slower chemical reaction without the same level of incendiary hazard. WP creates faster, more intense smoke but with greater fire risk, while HC produces a longer-lasting but less intense smoke cloud without the burning particle hazard.

Q: Why does white phosphorus continue to burn even when submerged in water? A: White phosphorus ignites spontaneously when exposed to oxygen at relatively low temperatures (around 30°C/86°F). While water can temporarily suppress burning by excluding oxygen, the phosphorus itself does not require oxygen from the air—the reaction is exothermic enough to continue underwater in certain conditions, and will reignite immediately when removed from water and exposed to air. This is why WP wounds are particularly dangerous and why the standard treatment involves keeping WP particles submerged or covered until they can be surgically removed.

Q: How can the M1 Smoke Projectile be distinguished from the M1 High Explosive round? A: The primary identification feature is the yellow band painted around the projectile body, indicating a smoke/screening agent fill. The M1 HE round typically has olive drab coloring with yellow stenciling indicating “HE” and may lack the yellow band. Additionally, smoke rounds are stenciled with “SMOKE WP” or “SMOKE HC” on the body. However, weathering and corrosion can obscure these markings, so any unidentified 105mm projectile should be treated as hazardous until positively identified by qualified personnel.

Q: What makes unfired M1 Smoke rounds hazardous as UXO? A: Unfired rounds present multiple hazards: the fuze may have degraded over decades, potentially becoming more sensitive to handling; the projectile body may have corroded, potentially exposing the WP fill to air (causing spontaneous ignition); and aged white phosphorus can form more unstable compounds. Even if the round appears intact, internal deterioration may not be visible. The combination of explosive, chemical, and incendiary hazards makes the M1 Smoke particularly dangerous as UXO.

Q: Why was the bursting smoke design preferred over base-ejection designs in some tactical situations? A: Bursting smoke rounds like the M1 produce immediate smoke effects upon impact—the smoke screen begins forming within seconds. Base-ejection rounds eject smoke canisters that fall more slowly and produce smoke over a longer period but with a delayed start. For urgent tactical needs such as immediate concealment of a unit under fire, emergency screening of a casualty evacuation, or rapid target marking, the instantaneous effect of bursting smoke was preferred. Base-ejection rounds were better suited for sustained screening operations where a longer-duration smoke cloud was needed.

Q: What is the recommended response when encountering a suspected M1 Smoke Projectile as UXO? A: The standard UXO response protocol applies: do not approach, touch, or disturb the item; mark the location if possible without approaching; withdraw to a safe distance; and report to qualified military EOD or civilian bomb disposal authorities. M1 Smoke rounds present multiple simultaneous hazards (explosive, incendiary, chemical/toxic), making them particularly dangerous. If the projectile body appears damaged or if white/yellow material is visible (potentially exposed WP), evacuate the area immediately and be aware that spontaneous ignition may occur.

Q: How does the fuze arming mechanism prevent accidental detonation during transport and handling? A: The fuzes used with the M1 employ multiple safety mechanisms. Bore safety features prevent the firing train from aligning until the projectile experiences the acceleration of being fired. Centrifugal (spin) arming requires the rotation imparted by the rifled gun barrel before final arming occurs. These combined “setback and spin” requirements ensure the fuze cannot arm until it has been properly fired from the gun, providing reasonable safety during transport and handling. However, aged fuzes may have degraded safety mechanisms, which is why UXO should never be assumed safe.

Q: Were there any documented cases of the M1 being used deliberately for its incendiary rather than smoke effects? A: Yes, white phosphorus munitions including the M1 Smoke were sometimes employed deliberately for their incendiary effects, particularly against fortified positions, bunkers, and structures. In the Pacific Theater, WP rounds were used against Japanese defensive positions where the combination of smoke (to obscure vision slits) and incendiary effects (to ignite wooden structures and create casualties) proved tactically effective. This dual-use nature of WP munitions has contributed to ongoing international discussions about their employment, though they remain legal when used primarily for smoke screening purposes.

SAFETY NOTICE: This lesson is intended for educational and training purposes. All ordnance should be considered dangerous until proven safe by qualified personnel. Unexploded ordnance should never be handled by untrained individuals—report findings to military or law enforcement authorities.