US M136 84mm HEAT Projectile

Overview

The M136 AT4 is a portable, single-shot, disposable 84mm anti-armor weapon system that fires a fin-stabilized High-Explosive Anti-Tank (HEAT) projectile. Developed as a replacement for the M72 LAW (Light Anti-armor Weapon), the M136 provides infantry units with a lightweight, effective means of engaging armored vehicles, fortifications, and hardened targets at close to medium ranges. The weapon system is preloaded, requiring no assembly in the field, and is discarded after a single use.

The M136 designation refers specifically to the US military variant of the Swedish-designed AT4, which has become one of the most widely used shoulder-launched anti-armor weapons in the world.

Country/Bloc of Origin

  • Primary Developer: Sweden (Saab Bofors Dynamics, formerly FFV/Bofors)
  • US Designation: M136 AT4
  • Development Period: Late 1970s to early 1980s
  • US Adoption: 1987
  • Licensed Production: Manufactured in the United States by ATK (now Northrop Grumman Innovation Systems) under license from Saab

The M136 represents a collaborative effort between Swedish weapons engineering and American defense procurement, resulting in one of the most successful anti-armor weapons of the late Cold War and post-Cold War period.

Ordnance Class

  • Type: Shoulder-launched, unguided anti-armor rocket
  • Primary Role: Anti-tank / anti-armor weapon
  • Secondary Role: Bunker/fortification defeat
  • Delivery Method: Man-portable, shoulder-fired
  • Guidance: Unguided (ballistic trajectory with fin stabilization)
  • Propulsion: Solid-propellant rocket motor

Ordnance Family/Nomenclature

Official Designations:

  • US Military: M136 AT4
  • Swedish Military: Pansarskott m/86 (Pskott m/86)
  • NATO Designation: AT4

Variants in the AT4 Family:

  • AT4 (M136): Standard HEAT variant
  • AT4 CS (Confined Space): Reduced backblast for urban/enclosed use
  • AT4 CS HP: Confined space, high penetration variant
  • AT4 CS ER: Confined space, extended range variant
  • AT4 CS HE: Confined space, high explosive (anti-personnel/structure)
  • AT4 CS AST: Anti-Structure Tandem warhead
  • AT4-HS: “Hang fire Safe” variant with improved safety mechanisms

NSN (National Stock Number): 1010-01-226-5943 (M136)

Related Training Variants:

  • M287 (9mm Tracer Trainer): Subcaliber training device
  • M136 Field Handling Trainer: Inert drill round

Hazards

Primary Hazards:

  • Explosive Hazard: The HEAT warhead contains approximately 440 grams of Octol (HMX/TNT mixture) explosive fill. Detonation produces a superplastic jet capable of penetrating steel armor.
  • Backblast Hazard: Upon firing, a dangerous backblast zone extends approximately 60 meters (200 feet) directly behind the weapon. Within this zone:
    • 0-15 meters: Lethal zone – death or severe injury
    • 15-60 meters: Danger zone – potential for burns, blast overpressure injury, and debris hazards
  • Rocket Motor Hazard: The solid propellant motor burns at extremely high temperatures. Misfire or hangfire conditions present significant risk of delayed ignition.
  • Impact Sensitivity: The piezoelectric fuze is designed to function on impact. While safety mechanisms prevent premature detonation, damaged or deteriorated rounds may have compromised safety features.

UXO Considerations:

Unexploded M136 projectiles present extreme hazards:

  • The piezoelectric fuze may remain armed and sensitive to movement
  • Impact damage may have compromised the warhead casing without detonating the explosive
  • Environmental exposure can degrade safety mechanisms over time
  • Never approach, touch, or move a suspected dud M136 projectile

Special Hazards:

  • The shaped charge jet has residual penetrating capability beyond the primary target
  • Spall (secondary fragmentation from target material) presents hazards to personnel behind struck armor
  • Propellant residue from unfired or misfired weapons may be toxic

Key Identification Features

Dimensions:

  • Overall Length (Launcher): 1,020 mm (40 inches)
  • Projectile Caliber: 84 mm
  • Weight (Complete System): 6.7 kg (14.8 lbs)
  • Projectile Weight: Approximately 1.8 kg (4 lbs)

External Features:

  • Launcher Tube: Fiberglass-wound composite tube, olive drab or tan coloration depending on production lot
  • Front End: Protective nose cap covering the projectile; must be removed before firing
  • Rear End: Rubber venturi (blast nozzle) with protective cover
  • Sighting System: Folding front and rear sights; front sight post, rear sight aperture with range markings
  • Carrying Sling: Attached shoulder sling for transport

Color Codes and Markings:

  • Launcher Body: Olive drab (OD) green or desert tan
  • Projectile Color: Olive drab with black markings (live HEAT)
  • Markings Include:
    • “ROCKET 84mm HEAT M136” (or similar nomenclature)
    • Lot number and date of manufacture
    • WARNING labels regarding backblast
    • Temperature limits for storage and use
    • Manufacturer identification

Projectile Characteristics:

  • Ogive-shaped nose with piezoelectric impact fuze
  • Six spring-loaded stabilizing fins (deploy upon leaving launcher)
  • Copper-lined shaped charge warhead

Fuzing Mechanisms

Primary Fuze Type: Piezoelectric impact fuze (point-detonating)

Arming Sequence:

  1. Safety Position: In the carried/stored configuration, multiple mechanical safeties prevent the firing mechanism from engaging:
    • Transport safety pin
    • Cocking lever in safe position
    • Sights folded down
  2. Preparation to Fire:
    • Remove front nose cap and rear venturi cover
    • Extend sights (cocking lever moves to intermediate position)
    • Remove transport safety pin
  3. Arming:
    • Upon firing, the rocket motor propels the projectile from the launcher
    • Setback forces and acceleration arm the fuze
    • Stabilizing fins deploy automatically upon exiting the launcher
    • Fuze is fully armed after traveling a safe distance from the firer (approximately 10 meters)

Fuze Functioning:

  • The piezoelectric crystal generates an electrical charge upon impact
  • This charge initiates the detonator, which in turn detonates the main explosive fill
  • Designed to function at oblique impact angles up to 65 degrees from perpendicular

Safety Mechanisms:

  • Mechanical safety blocks prevent firing pin movement until proper acceleration is achieved
  • Out-of-line detonator train until armed
  • No self-destruct mechanism – unexploded rounds remain hazardous indefinitely

Misfire Procedures: In the event of a misfire (trigger pulled but no ignition):

  1. Maintain aim downrange for 60 seconds minimum
  2. If round does not fire, lower weapon carefully
  3. Follow unit SOP for misfire handling
  4. Do not attempt to disassemble or repair

History of Development and Use

Development Background:

The M136 AT4 emerged from Sweden’s efforts to develop a replacement for the aging Miniman (Pansarskott m/68) anti-tank weapon in the late 1970s. Saab Bofors (then FFV) designed the AT4 to provide infantry with a lightweight, powerful weapon capable of defeating modern main battle tank armor from the side and rear, as well as lighter armored vehicles from any angle.

US Adoption:

The United States Army sought a replacement for the M72 LAW (Light Anti-armor Weapon) during the early 1980s. The M72, while revolutionary when introduced, had become inadequate against increasingly sophisticated Soviet armor featuring composite protection and explosive reactive armor (ERA).

Following competitive evaluation, the US Army selected the AT4 in 1984, with the weapon entering service as the M136 in 1987. The AT4 offered:

  • Significantly improved penetration over the M72 LAW
  • Greater effective range
  • More reliable fuzing and propulsion
  • Improved accuracy through better sights and fin stabilization

Combat Employment:

The M136 has seen extensive combat use across multiple conflicts:

  • Operation Just Cause (Panama, 1989): First US combat use; employed against fortified positions and vehicles
  • Gulf War (1990-1991): Used extensively against Iraqi armored vehicles and bunkers
  • Somalia (1993): Employed in urban combat during the Battle of Mogadishu
  • Afghanistan (2001-2021): Widely used against fortifications, caves, and vehicles
  • Iraq (2003-2011): Standard infantry anti-armor weapon throughout the conflict
  • Various other deployments by US and allied forces worldwide

Evolution:

The success of the basic M136 led to development of specialized variants:

  • The AT4 CS (Confined Space) variant was developed for urban warfare, using a saltwater countermass to reduce backblast
  • Tandem warhead versions were developed to defeat ERA-equipped vehicles
  • Extended range and improved penetration variants continue to be developed

Current Status:

  • Remains in active service with the US military and over 40 nations
  • Continues to be manufactured and improved
  • Over 600,000 produced for worldwide distribution

Technical Specifications

SpecificationValue
Caliber84 mm
Overall Length1,020 mm (40 in)
Weight (Loaded)6.7 kg (14.8 lbs)
Muzzle Velocity290 m/s (950 ft/s)
Effective Range300 m (point target)
Maximum Range500 m (area target); 2,100 m maximum flight
Armor Penetration>420 mm RHA (Rolled Homogeneous Armor)
Explosive Fill440 g Octol (HMX/TNT)
Operating Temperature-40°C to +60°C (-40°F to +140°F)
Shelf Life10+ years (properly stored)
Time to Fire<10 seconds (from carry to fire)

Penetration Performance:

  • The shaped charge can defeat approximately 420 mm of steel armor at 0 degrees obliquity
  • Effective against concrete up to 500 mm thick
  • Can penetrate 1.8 m (6 ft) of sandbags or soil

Frequently Asked Questions

Q: Why was the M136 AT4 chosen to replace the M72 LAW? A: The M136 offered substantially improved armor penetration (420+ mm vs. approximately 300 mm for the M72), greater accuracy through fin stabilization and improved sights, better reliability, and longer effective range. As Soviet armor improved throughout the 1970s and 1980s with composite armor and ERA, the M72’s capabilities became marginal against front-line threats. The AT4 restored infantry’s ability to effectively engage armored vehicles from multiple angles.

Q: Can the M136 defeat modern main battle tanks? A: The M136’s penetration of 420+ mm RHA is insufficient to defeat the frontal armor of modern MBTs like the M1 Abrams, Leopard 2, or T-90, which feature composite armor and ERA providing protection equivalent to 800+ mm RHA. However, the M136 remains effective against the side and rear armor of most MBTs, and is highly effective against lighter armored vehicles (APCs, IFVs), fortifications, and structures. For heavy armor threats, weapons like the FGM-148 Javelin provide the necessary penetration.

Q: What makes the AT4 CS variant suitable for confined spaces? A: Standard recoilless weapons like the M136 produce a dangerous backblast that makes firing from enclosed spaces (rooms, bunkers, vehicles) impossible without risk of injury to the operator. The AT4 CS uses a countermass of saltwater contained in a plastic container that is expelled rearward upon firing. This countermass absorbs much of the propellant energy, reducing the backblast danger zone to approximately 20 meters in open terrain, and allowing safe firing from within structures with adequate room volume.

Q: How does the piezoelectric fuze work, and why is it preferred for this application? A: The piezoelectric fuze contains a crystal that generates an electrical charge when subjected to mechanical stress (impact). Upon striking the target, the crystal is compressed, generating sufficient voltage to fire an electric detonator. This type of fuze is preferred because it is extremely reliable, functions instantaneously on impact, does not require batteries, has an indefinite shelf life, and is insensitive to most environmental conditions. Its instantaneous functioning is critical for shaped charge warheads, which must detonate at the optimal standoff distance.

Q: What is the proper procedure if an M136 fails to fire? A: If the trigger is pulled and the weapon does not fire (misfire), the operator must: (1) Maintain the weapon aimed downrange for a minimum of 60 seconds to allow for possible hangfire (delayed ignition); (2) If the weapon still has not fired, carefully lower it while keeping it pointed in a safe direction; (3) Do not attempt to re-cock or re-fire the weapon; (4) Mark the weapon as a dud and follow unit SOP for evacuation or disposal. Misfired M136s should be treated as unexploded ordnance and handled only by qualified EOD personnel.

Q: Why does the M136 have no self-destruct mechanism? A: Unlike some guided missiles and submunitions, the M136 projectile does not incorporate a self-destruct (SD) or self-neutralization (SN) feature. This is primarily because: (1) The weapon is relatively simple in design, and adding SD mechanisms would increase complexity and cost; (2) The fuze is highly reliable, with dud rates well under 5%; (3) The weapon is typically employed at relatively close range against point targets, where duds can be more easily marked and cleared. However, this means that M136 duds remain hazardous indefinitely and require proper EOD procedures for disposal.

Q: How do the projectile’s fins deploy, and what purpose do they serve? A: The M136 projectile has six spring-loaded fins that are folded against the body while the projectile is inside the launcher tube. Upon exiting the muzzle, the fins spring outward into their deployed position. These fins serve two purposes: (1) They provide aerodynamic stability through spin (the fins are canted slightly to impart rotation), keeping the projectile oriented nose-forward throughout its flight; (2) They keep the projectile’s trajectory predictable for accurate engagement. Without stabilization, the projectile would tumble, drastically reducing accuracy and potentially preventing proper fuze functioning.

Q: What training devices exist for the M136, and why are they important? A: The primary training device is the M287 9mm Tracer Trainer, which is a reusable launcher that fires 9mm tracer rounds to simulate the M136’s trajectory. This allows soldiers to practice aiming, range estimation, and fire discipline without expending expensive live rounds. Additionally, Field Handling Trainers (completely inert replicas) are used for teaching loading procedures, carrying techniques, and safety protocols. Training devices are critical because the live M136 is single-shot and disposable—soldiers cannot practice with the actual weapon without consuming it.

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.