US M57 Firing Device
Overview
The M57 Electrical Firing Device, commonly known as the “Clacker,” is an American hand-held pulse generator designed to remotely detonate the M18A1 Claymore antipersonnel mine and other electrically-initiated explosive devices. This iconic device converts mechanical energy into electrical energy through a simple squeeze action, generating sufficient voltage to initiate electric blasting caps at distances up to 100 feet. The M57’s distinctive “clacking” sound during operation and its association with the Claymore mine have made it one of the most recognizable pieces of military demolition equipment, particularly from its extensive use during the Vietnam War.
Country/Bloc of Origin
- Country: United States of America
- Development Period: Late 1950s to early 1960s
- Development Designation: T49E1
- Developer: U.S. Army Ordnance Corps / Picatinny Arsenal
- Service Entry: Standardized in the early 1960s
- Manufacturers: Various U.S. defense contractors (government-furnished equipment)
- Allied Use: Supplied to NATO allies, Australia, South Korea, South Vietnam, and numerous partner nations
Ordnance Class
- Type: Electrical Firing Device / Hand-Held Pulse Generator
- Primary Role: Remote electrical initiation of Claymore mines and demolition charges
- Category: Demolition initiating equipment
- Power Generation: Mechanical-to-electrical energy conversion (dynamo principle)
Ordnance Family/Nomenclature
- Official Designation: Firing Device, Electrical: M57
- Development Designation: T49E1
- Common Name: “Clacker” (universal military slang)
- NSN: Various (by manufacturer/lot)
- Associated Equipment:
- M18A1 Claymore Mine: Primary application
- M4 Electric Blasting Cap Assembly: Standard initiator for Claymore
- M40 Test Set: Used to verify M57 function and circuit continuity
- M57 Firing Wire: 100-foot two-conductor wire (included with Claymore)
- Related Firing Devices:
- M34 Blasting Machine: 30-cap capacity for larger demolition operations
- M32 Blasting Machine: 10-cap capacity
- M122 Demolition Firing Device: Radio-controlled remote firing system
Hazards
Primary Hazards
- Electrical Output: Generates 3-volt double pulse capable of initiating electric blasting caps
- Premature Initiation Risk: Accidental activation can detonate connected explosives
- No Explosive Content: The M57 itself contains no explosives
Safety Considerations
- Always treat as capable of firing even if believed to be non-functional
- Never connect to live circuit until ready to fire
- Maintain safety bail in locked position until firing is imminent
- Test with M40 Test Set before connecting to explosive circuit
- Keep dust cover on electrical connector when not in use
- Positive control: Only the designated firer should possess the M57
Electrical Hazards
- Static Electricity: Standard ESD precautions apply when handling electric blasting caps
- RF Hazards: Electric blasting caps may be susceptible to radio frequency initiation; maintain prescribed distances from RF transmitters
- Stray Current: Ensure no stray electrical currents in vicinity when connecting firing circuit
Handling Precautions
- Inspect rubber plunger and connector for damage before use
- Do not disassemble or attempt repair—return damaged units for replacement
- Protect from moisture, dirt, and physical abuse
- Store in carrying case or bandoleer pocket when not in use
Circuit Safety
- Always short-circuit (shunt) blasting cap leads until ready to connect
- Test firing circuit continuity with M40 Test Set before connecting M57
- Maintain minimum safe distances before firing
- Call “FIRE IN THE HOLE” three times before initiating
Key Identification Features
Physical Characteristics
- Shape: Rectangular box with integral handle/lever
- Material: Molded plastic body (typically fiberglass-reinforced); metal internal components
- Color: Olive drab green (standard military); some training/late production variants in clear plastic
- Weight: Approximately 1 pound (0.45 kg)
Dimensions
- Length: 105 mm (4.1 inches)
- Width: 35 mm (1.4 inches)
- Height: 90 mm (3.5 inches)
External Features
- Handle/Lever: Hinged at top; squeezed to generate electrical pulse
- Rubber Plunger/Button: Located beneath handle; compressed when handle is squeezed
- Safety Bail: Steel bar that locks handle in safe position; must be rotated to allow firing
- Electrical Connector: Two-pole male connector on front face
- Dust Cover: Protective cap over connector (attached by lanyard or integral)
- Body Markings: Model designation, lot number, manufacturer, date
Markings (Typical)
FIRING DEVICE ELECTRICAL M57
LOT [XXX-X-XX]
MFG [XX-XX]
[Manufacturer Symbol]
Distinguishing Features
- Distinctive rectangular “hand grenade” profile
- Olive drab coloration (clear plastic variants exist)
- Characteristic hinged handle design
- Two-pole electrical connector matching M18A1 firing wire
Fuzing Mechanisms
Operating Principle
The M57 is an electromechanical pulse generator based on the dynamo principle. It converts mechanical energy (squeezing the handle) into electrical energy through electromagnetic induction.
Internal Components
- Permanent Magnets: Create magnetic field
- Armature/Coil Assembly: Rotating armature passes through magnetic field
- Triggering Mechanism: Handle compression drives armature rotation
- Spring Return: Returns handle to ready position after firing
- Electrical Contacts: Transfer generated pulse to output connector
Electrical Output
- Voltage: Approximately 3 volts (double pulse—one positive, one negative)
- Current: Sufficient to fire up to five M6 electric blasting caps in series at 100 feet
- Pulse Type: Momentary pulse (not sustained current)
- Polarity: Bipolar (both positive and negative pulses generated)
Functioning Sequence
- Safe Condition: Safety bail locked over handle prevents compression
- Arm: Rotate safety bail away from handle
- Prepare: Grip device firmly in hand
- Fire: Squeeze handle sharply and completely
- Handle compresses rubber plunger
- Plunger drives armature through magnetic field
- Electromagnetic induction generates electrical pulse
- Pulse travels through connected wire to blasting cap
- Blasting cap bridge wire heats and initiates explosive charge
- Reset: Release handle; spring returns mechanism to ready position
Capacity
- Standard Rating: Five M6 electric blasting caps in series
- Effective Range: 100 feet of standard firing wire (M57 firing wire)
- Circuit Configuration: Series circuit only (parallel circuits not recommended)
Safety Features
- Safety Bail: Physical lock prevents handle compression
- Dust Cover: Protects connector from contamination and accidental contact
- Visual Inspection: Clear indicators of safe/armed status
- Deliberate Action Required: Full handle squeeze needed for firing
History of Development and Use
Development Background
The M57 Electrical Firing Device was developed in the late 1950s as part of the M18A1 Claymore mine system. The Claymore concept required a reliable, simple, and portable means of command detonation that could be operated by individual soldiers. The resulting T49E1 (standardized as M57) met these requirements through its innovative dynamo design, which eliminated the need for batteries while providing reliable electrical output under field conditions.
Design Philosophy
The M57 was designed with several key principles:
- Simplicity: No batteries, no complex mechanisms, minimal training required
- Reliability: Mechanical generation ensures function regardless of battery condition
- Portability: Lightweight, compact design fits in ammunition pouch or cargo pocket
- Durability: Robust construction withstands field abuse
- Safety: Multiple safety features prevent accidental firing
Vietnam War Service
The M57 achieved iconic status during the Vietnam War (1962-1975), where the M18A1 Claymore became one of the most widely used defensive weapons. American forces employed Claymores extensively for:
- Perimeter defense of fire bases and patrol bases
- Ambush operations
- Night defensive positions (NDPs)
- Mechanical ambush (trip-wire activated with M57 for command backup)
- Convoy protection
The distinctive “clacking” sound of the M57 became synonymous with the Claymore mine, and the device earned its enduring nickname from this characteristic noise.
Post-Vietnam Evolution
Following Vietnam, the M57 remained in service with minimal modification. The basic design proved so effective that major redesign was unnecessary. Minor improvements included:
- Material refinements for increased durability
- Connector redesigns for improved reliability
- Quality control enhancements
- Training variant production (clear plastic bodies for instructional purposes)
Global Proliferation
The M57 and M18A1 system was provided to numerous U.S. allies, leading to widespread adoption. The device saw service in:
- Korean Peninsula (ongoing)
- Central America (1980s)
- Persian Gulf (1991, 2003)
- Afghanistan (2001-2021)
- Iraq (2003-2011)
- Various peacekeeping and counterinsurgency operations worldwide
Current Status
- U.S. Army Classification: Standard
- Active Service: Remains in front-line service with U.S. and allied forces
- Production: Continues under various contracts
- Training: Included in basic combat engineer and infantry training
- Modernization: No significant replacement program; proven design remains effective
Cultural Impact
The M57 “Clacker” has achieved significant cultural recognition beyond military circles:
- Featured prominently in Vietnam War films and literature
- Included in numerous video games depicting Vietnam and modern conflicts
- Collected by militaria enthusiasts (demilitarized versions)
- Referenced in military slang and terminology
Technical Specifications
| Parameter | Specification |
|---|---|
| Designation | Firing Device, Electrical: M57 |
| Development Designation | T49E1 |
| Common Name | “Clacker” |
| Type | Hand-held electrical pulse generator |
| Power Source | Mechanical (dynamo) |
| Output Voltage | 3 volts (double pulse, ±) |
| Capacity | Five M6 electric blasting caps in series |
| Effective Range | 100 feet (with standard firing wire) |
Physical Specifications
| Parameter | Specification |
|---|---|
| Length | 105 mm (4.1 in) |
| Width | 35 mm (1.4 in) |
| Height | 90 mm (3.5 in) |
| Weight | Approximately 0.45 kg (1 lb) |
| Body Material | Molded plastic (fiberglass-reinforced) |
| Color | Olive drab green (standard) |
| Connector Type | Two-pole male |
Operating Specifications
| Parameter | Specification |
|---|---|
| Operating Temperature | -40°F to +125°F (-40°C to +52°C) |
| Firing Action | Handle squeeze (sharp, complete compression) |
| Safety Mechanism | Rotating safety bail |
| Testing | M40 Test Set |
| Service Life | Extended (no batteries to expire) |
Associated Equipment (M18A1 Claymore System)
| Component | Designation |
|---|---|
| Mine | M18A1 Claymore Antipersonnel Mine |
| Blasting Cap Assembly | M4 Electric Blasting Cap Assembly |
| Firing Wire | 100-foot two-conductor |
| Test Set | M40 |
| Carrying Bandoleer | M7 |
Electrical Circuit Requirements
| Parameter | Specification |
|---|---|
| Circuit Type | Series (required) |
| Maximum Caps | 5 × M6 in series |
| Wire Resistance | Maximum per circuit specifications |
| Testing | Required before connecting M57 |
Frequently Asked Questions
Q: Why is the M57 called a “Clacker”? A: The nickname comes from the distinctive “clacking” sound produced when the handle is squeezed. As the armature rapidly rotates through the magnetic field, it creates an audible mechanical noise. This sound became so associated with the device during Vietnam War service that “clacker” became the universal military term, largely replacing the official designation in everyday use.
Q: How does the M57 generate electricity without batteries? A: The M57 operates on the dynamo principle (electromagnetic induction). When the handle is squeezed, it drives a coiled armature through a magnetic field created by permanent magnets. This relative motion between conductor and magnetic field induces an electrical current in the armature windings. The mechanical energy of your hand squeeze is converted directly into electrical energy—the same principle used in hand-crank generators and bicycle dynamos.
Q: Can the M57 fire devices other than Claymore mines? A: Yes. The M57 can initiate any electrically-fired explosive device that uses compatible electric blasting caps (such as the M6) within its capacity (five caps in series at 100 feet). This includes demolition charges, breaching charges, and other command-detonated munitions. However, the M57 is specifically designed and optimized for the M18A1 Claymore system.
Q: Why is circuit testing with the M40 Test Set required before connecting the M57? A: Circuit testing verifies that the firing circuit has proper continuity (no breaks in the wire) and acceptable resistance before the firing device is connected. A faulty circuit could result in failure to fire (misfire), which creates an extremely dangerous unexploded ordnance situation. The M40 Test Set uses very low current that cannot initiate a blasting cap, making it safe to use on live circuits. Never connect the M57 to a circuit that hasn’t been tested.
Q: What happens if the M57 doesn’t fire the Claymore? A: A misfire creates a dangerous situation requiring specific procedures: (1) Keep the M57 connected and aimed at the target; (2) Wait a prescribed period (minimum 30 seconds for electric circuits); (3) Attempt to refire if tactically appropriate; (4) If still unsuccessful, treat as unexploded ordnance; (5) Follow unit SOPs for misfire procedures. Never approach a misfired Claymore immediately—the circuit may be intermittent, and the mine could detonate during approach.
Q: Can the M57 be used underwater? A: The standard M57 is not waterproof and should not be submerged. Moisture intrusion can damage internal components and prevent proper function. However, the M18A1 Claymore system includes provisions for water-resistant operation, and specialized sealing methods exist for underwater demolition applications. For amphibious or wet environment operations, consult applicable technical manuals for waterproofing procedures.
Q: How can you tell if an M57 is functional? A: The M40 Test Set is the approved method for testing M57 function. Connect the M40 to the M57’s output connector and squeeze the handle. The test set indicates whether adequate current is being generated. Additionally, physical inspection should verify: (1) Handle moves freely and returns to position; (2) Safety bail functions properly; (3) Rubber plunger is intact and resilient; (4) Connector is clean and undamaged; (5) No visible damage to body. If any doubt exists, replace the M57 with a known-good unit.
Q: Why does the M57 produce a “double pulse” (positive and negative)? A: The bipolar pulse results from the armature’s interaction with the magnetic field. As the armature accelerates through the field in one direction, it generates a pulse of one polarity. The design produces both positive and negative pulses to ensure reliable initiation regardless of how the firing wire is connected (polarity doesn’t matter for standard electric blasting caps). This design feature increases reliability and simplifies field use.
Q: Are there training versions of the M57 available? A: Yes. Training and demonstration versions of the M57 exist, including units with clear plastic bodies that allow internal mechanism observation during instruction. Additionally, non-functional (demilitarized) M57s are available for display and familiarization training. Some units use fully functional M57s with inert training Claymores for realistic training scenarios. Always verify the status (live vs. training) of any firing device before handling.
Q: How does the M57 compare to battery-powered blasting machines? A: The M57 offers several advantages over battery-powered alternatives: (1) No batteries to fail, expire, or require replacement; (2) Lighter weight; (3) More compact; (4) Unlimited “shelf life” for power source; (5) Immediate readiness. However, battery-powered blasting machines offer greater capacity (more blasting caps), higher voltage for longer wire runs, and sustained current output. The M57 is optimized for the single-device/short-range mission profile of Claymore employment, while larger blasting machines serve broader demolition requirements.
Safety Notice
All ordnance items should be considered dangerous until proven safe by qualified Explosive Ordnance Disposal (EOD) personnel. The M3 firing device is particularly hazardous due to its tension-release capability—standard wire-cutting neutralization techniques WILL cause initiation. Never attempt to handle, disarm, or move suspected ordnance. Mark the location, evacuate the area, and report findings to military or law enforcement authorities immediately.
This information is provided for educational and identification training purposes only.