US M57 “Clacker” Firing Device

Overview

The M57 Firing Device, universally known as the “Clacker” due to its distinctive sound when activated, is a hand-held electrical firing device that generates a piezoelectric impulse to initiate electric blasting caps. Primarily associated with the M18A1 Claymore antipersonnel mine, the M57 has become one of the most recognizable pieces of US military demolition equipment.

The M57’s simple, reliable design makes it the standard method for command-detonating Claymore mines and initiating other electrically-fired demolition charges from a protected position. Its piezoelectric operation requires no batteries, ensuring reliability even after extended storage.

Country/Bloc of Origin

• Country: United States of America
• Developer: US Army (developed alongside the M18A1 Claymore mine system)
• Service Entry: Early 1960s
• Primary Users: US Army, US Marine Corps, US Navy SEALs, Allied nations
• Manufacturer: Various defense contractors

The M57 was developed as part of the complete Claymore mine system to provide a simple, reliable means of command detonation. Its development was driven by the need for an individual-soldier-operated firing device that would function reliably without batteries in the tropical environment of Southeast Asia.

Ordnance Class

• Type: Electrical firing device / Piezoelectric initiator
• Primary Role: Command detonation of Claymore mines and demolition charges
• Category: Demolition accessory / Mine firing system component
• Operation: Piezoelectric pulse generation

The M57 is not an explosive item but is an essential component of explosive systems. It is classified as a demolition accessory and is controlled as part of the Claymore mine system or as a separate line item for general demolition use.

Ordnance Family/Nomenclature

Official Designation:

• US Military: Firing Device, Electrical, M57
• Common Name: “Clacker” (onomatopoeia from sound of operation)

Claymore Mine System Components:

• M18A1 Claymore Mine: The anti-personnel mine the M57 is designed to fire
• M57 Firing Device: The subject device
• M40 Test Set: Tests M57 output and Claymore circuit continuity
• Firing Wire (M4 Blasting Cap Assembly): 100-foot wire with electric blasting cap
• Bandoleer: Carrying case for complete Claymore system

Related Firing Devices:

• M34 Blasting Machine: 10-cap capacity, hand-crank generator
• M32 Blasting Machine: Single-cap, twist-type generator
• M142 Firing Device: Similar electrical firing device
• M152 Firing Device: Enhanced version for special applications

NSN (National Stock Number): 1375-00-028-5674

Hazards

Primary Hazards:

The M57 itself contains no explosive material but presents hazards through its function:

• Electrical Output Hazard: The piezoelectric generator produces sufficient voltage to initiate blasting caps. Accidental contact between the output leads and a blasting cap or sensitive detonator will cause immediate detonation.
• System Initiation Hazard: When connected to a Claymore mine or demolition charge, the M57 represents the trigger for a significant explosive system. Premature or unintended activation initiates the connected explosive.
• Command Detonation Risks: Unlike victim-operated devices, the M57-initiated system detonates when the operator chooses. This creates fratricide risk if friendly forces enter the kill zone before firing or if firing occurs without proper clearance.

Safety Considerations:

• Never connect the M57 to a live circuit until ready to fire
• Always use the M40 Test Set to verify circuit continuity before connecting the M57
• Keep the safety bail engaged until the firing decision is made
• Store firing devices separately from blasting caps and demolition equipment
• Ensure all personnel are clear of the danger area before firing

Misfire Hazards:

• If the M57 fails to detonate the charge, wait a minimum of 30 seconds before re-attempting
• Multiple failed attempts suggest a circuit problem—wait 30 minutes before approaching
• Never approach a misfired Claymore mine; destroy it in place if possible

UXO Considerations:

• An M57 found in the field may be connected to unfired Claymore mines or demolition charges
• Never pull or manipulate firing wire connected to abandoned M57s
• Assume any M57 in an unsecured area is connected to live explosives

Key Identification Features

Dimensions:

• Length: Approximately 114 mm (4.5 inches)
• Width: Approximately 67 mm (2.6 inches)
• Height: Approximately 43 mm (1.7 inches)
• Weight: Approximately 227 grams (8 oz)

External Features:

• Housing: Olive drab (OD) green or black plastic case
• Hand Grip: Ergonomic squeeze grip for one-handed operation
• Safety Bail: Wire bail that prevents accidental actuation when in safe position
• Output Terminals: Two wire connection points (typically screw posts or quick-connect)
• Carrying Hole: Opening for lanyard or carrying attachment

Mechanical Description:

• Squeeze Handle: The movable actuator that compresses the piezoelectric element
• Piezoelectric Crystal: Generates electrical pulse when mechanically stressed
• Return Spring: Returns handle to ready position after actuation
• Contact Points: Complete circuit through output terminals when actuated

Markings:

• “FIRING DEVICE M57” molded into case
• “CLACKER” (unofficial, sometimes added)
• Manufacturer identification
• Lot number and date of manufacture
• NSN may be present
• Safety instructions

Distinctive Characteristics:

• Compact size fits in one hand
• Distinctive “clack” sound when squeezed (hence nickname)
• Wire bail safety clearly visible
• OD green color (standard military finish)

Fuzing Mechanisms

Note: The M57 is not a fuzed munition but an electrical initiator. This section describes its operating mechanism.

Piezoelectric Operating Principle:

The M57 operates on the piezoelectric effect—certain crystals generate an electrical charge when mechanically stressed:

1. Rest Position: The piezoelectric crystal is unstressed; no electrical output
2. Actuation: Squeezing the handle rapidly compresses the crystal
3. Charge Generation: Mechanical compression produces a high-voltage electrical pulse
4. Transmission: The pulse travels through the output terminals and firing wire
5. Initiation: The pulse reaches the electric blasting cap, heating the bridgewire
6. Detonation: The heated bridgewire initiates the primary explosive in the blasting cap

Electrical Characteristics:

• Output Type: High-voltage, low-current pulse
• Voltage: Sufficient to reliably initiate M6/M7 electric blasting caps over 100+ meters of firing wire
• Pulse Duration: Momentary (milliseconds)
• No Battery Required: Piezoelectric operation is entirely mechanical-to-electrical conversion

Operating Sequence:

1. Preparation:
   • Connect firing wire to Claymore mine or demolition charge
   • Extend wire to firing position
   • Test circuit continuity with M40 Test Set
   • Take covered position facing the target
2. Ready to Fire:
   • Connect firing wire to M57 output terminals
   • Rotate safety bail out of the way
3. Fire:
   • Squeeze handle rapidly and firmly
   • The “clack” sound confirms actuation
   • Repeat if necessary (multiple squeezes are acceptable)

Safety Features:

• Safety Bail: A metal wire bail physically blocks handle movement when engaged across the grip
• Handle Return: Handle returns to start position, ready for re-actuation if needed
• Positive Action Required: Deliberate, firm squeeze needed—cannot fire from vibration or light pressure
• Visible Safety Status: Bail position clearly shows safe or ready-to-fire status

History of Development and Use

Development Background:

The M57 was developed in the early 1960s as part of the M18A1 Claymore mine system. The Claymore concept required a reliable command-detonation capability to ensure the mine would fire only when enemy personnel were within the kill zone and friendly forces were clear.

Requirements Driving Development:

• No Batteries: Batteries were unreliable in the humid tropical environment of Vietnam; a piezoelectric system eliminated this weakness
• Simplicity: Individual soldiers needed to employ the system without specialized training
• Reliability: The device had to function after being carried on patrols through jungle conditions
• Quick Action: The firing device had to allow immediate response when enemy forces appeared

Vietnam War Service:

The M57 became iconic during the Vietnam War:

• Claymore mines with M57 initiation were essential for defensive positions, ambushes, and patrol bases
• The distinctive “clacker” became synonymous with the Claymore system
• Soldiers developed various tactical techniques for Claymore employment
• The system proved highly effective against massed infantry attacks

Combat Effectiveness:

The M57/Claymore combination offered significant tactical advantages:

• Instantaneous response to enemy contact
• Precise timing under operator control
• Immunity to electronic countermeasures
• Reliable function in all weather conditions
• Psychological impact on enemy forces (fear of ubiquitous Claymores)

Evolution and Variants:

While the basic M57 design has remained largely unchanged, the system has been supplemented:

• Test equipment (M40) improved reliability verification
• Enhanced firing devices for special applications
• Integration with other initiation systems for complex demolition tasks
• Training versions for drill and instruction

Global Proliferation:

The success of the M57/Claymore system led to:

• Widespread adoption by US allies
• Licensed and unlicensed copies produced internationally
• Similar systems developed by other nations (Soviet MON-series with MDV initiators)
• Incorporation of the piezoelectric principle into other firing devices

Current Status:

• Remains standard US military issue
• Included in every M18A1 Claymore mine kit
• Used for general demolition beyond Claymore initiation
• Continues in production to support inventory requirements

Technical Specifications

Specification	Value
Length	114 mm (4.5 in)
Width	67 mm (2.6 in)
Height	43 mm (1.7 in)
Weight	227 g (8 oz)
Operating Principle	Piezoelectric pulse generation
Power Source	None required (mechanical-to-electrical conversion)
Output Voltage	High voltage pulse (sufficient for cap initiation)
Wire Compatibility	Standard 2-conductor firing wire
Effective Firing Distance	100+ meters through standard firing wire
Operating Temperature	-40°C to +60°C
Shelf Life	Indefinite (no battery degradation)

Reliability Characteristics:

• Functions reliably across extreme temperature range
• Resistant to moisture and humidity
• No maintenance required
• Multiple actuation cycles without degradation
• Consistent output across service life

Electrical Output:

• Designed to reliably initiate:
  • M6 Electric Blasting Cap
  • M7 Electric Blasting Cap (Special)
  • M4 Blasting Cap Assembly (Claymore system)
  • Commercial equivalent electric blasting caps

Frequently Asked Questions

Q: Why is the M57 called a “Clacker”? A: The name “Clacker” is onomatopoeia—it describes the distinctive “clack” sound produced when the device is actuated. When the handle is squeezed, the piezoelectric mechanism creates a sharp clicking or clacking noise. This sound became so associated with the device that “clacker” became its universal nickname among troops, often used more frequently than the official M57 designation. The sound also serves as audible confirmation that the device has been actuated.

Q: How does the M40 Test Set work with the M57? A: The M40 Test Set is a pocket-sized device used to verify the M57 and Claymore mine circuit before connecting for firing: (1) The test set can check the M57’s electrical output—when the M57 is squeezed with test leads connected, a neon bulb in the M40 flashes, confirming function; (2) The test set can check circuit continuity through the firing wire and blasting cap without providing enough current to initiate detonation; (3) Using the M40 before connecting the M57 to a live circuit identifies faulty components before they cause a misfire in combat. Proper procedure is to test the M57 first, then test the firing circuit with the M40, then connect the M57.

Q: Can the M57 be used for demolition charges other than Claymore mines? A: Yes, the M57 is a general-purpose electrical firing device that can initiate any standard military electric blasting cap. It is commonly used for: (1) Command-detonated demolition charges; (2) Ambush initiation of explosives; (3) Breaching charges when electrical initiation is preferred; (4) Any application requiring reliable electrical firing from a protected position. The M57 is particularly useful when batteries are impractical and when the charge needs to be fired at a precise moment under operator control.

Q: What happens if the M57 is squeezed but the charge doesn’t detonate? A: Misfire procedures for the M57/Claymore system are critical: (1) Wait 30 seconds and attempt to fire again with 2-3 firm squeezes; (2) If still unsuccessful, wait 30 minutes before approaching—the circuit may be compromised but could still function; (3) Do not attempt to troubleshoot or disconnect the circuit immediately; (4) After the waiting period, approach with caution; (5) If the charge cannot be safely recovered, destroy it in place with a new charge. Misfires are most often caused by damaged firing wire, corroded connections, or faulty blasting caps, not by M57 failure.

Q: Why doesn’t the M57 require batteries? A: The M57 uses a piezoelectric crystal that converts mechanical energy (squeezing) directly into electrical energy. When the crystal is rapidly compressed, it generates a high-voltage pulse without any external power source. This design provides several advantages: (1) No batteries to fail, leak, or require replacement; (2) Unlimited shelf life—the device is ready to use even after years of storage; (3) Reliable function in extreme temperatures where batteries might fail; (4) Reduced logistics burden (no battery resupply needed). This was especially important in Vietnam where heat and humidity quickly degraded batteries.

Q: How far can the M57 fire through firing wire? A: The M57 is rated to reliably initiate blasting caps at distances of 100 meters (330 feet) or more through standard 2-conductor firing wire. The limiting factors are: (1) Wire resistance—longer wire means more resistance; (2) Connection quality—corroded or loose connections reduce current flow; (3) Environmental conditions—wet connections can cause short circuits or current leakage. The standard Claymore firing wire assembly (M4) is 100 feet (30 meters), but the M57 can function through longer wire runs. For extended distances, wire gauge and connection quality become increasingly important.

Q: Is the M57 vulnerable to electronic countermeasures? A: No, the M57 is highly resistant to electronic countermeasures (ECM). Its operation is entirely passive—there is no radio frequency component, no electronic signal to jam, and no transmission that can be detected or interfered with. The only electronic event is the piezoelectric pulse traveling through a physical wire to the blasting cap. This makes the M57/Claymore system immune to the jamming devices used to defeat radio-controlled IEDs. The only way to defeat the M57 is to cut the firing wire or destroy the device itself.

Q: Can multiple charges be fired with one M57? A: Yes, the M57 can initiate multiple blasting caps wired in series, though there are practical limits: (1) Each additional cap increases circuit resistance; (2) The piezoelectric pulse must generate enough current to heat all bridgewires simultaneously; (3) Generally, 2-3 caps in series is reliable; more than that risks misfires; (4) Poor connections compound with each additional cap; (5) For large multi-charge demolitions, more powerful blasting machines (M34, M32) are recommended. When multiple Claymores are needed, they are typically wired to separate firing systems or to a higher-capacity generator.

Q: What is the proper way to store the M57? A: Proper M57 storage involves: (1) Safety bail in the engaged (safe) position; (2) Output terminals clean and free of corrosion; (3) Stored separately from blasting caps and explosives; (4) Protected from physical damage (crushing, dropping); (5) Clean and dry; (6) At moderate temperatures when possible (though extreme temperatures won’t damage it). The M57 has an indefinite shelf life because there are no batteries or perishable components. Before use after storage, function-check with an M40 Test Set to verify proper operation.

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.