US MK 55 Firing Device (Firing Device, Hand Held, MK 55 Mod 0)
Overview
The MK 55 Firing Device, officially designated Firing Device, Hand Held, MK 55 Mod 0, is a compact, single-tube, hand-held mechanical firing device used by the United States Navy and special operations forces to initiate shock tube-based demolition systems. The MK 55 is part of a family of Navy hand-held initiators designed for reliable, safe, and simple initiation of non-electric firing systems in field conditions. It provides EOD technicians, combat engineers, breachers, and special operations personnel with a rugged, portable means of firing shock tube-connected charges without the need for electrical power or complex equipment.
Country/Bloc of Origin
- Country: United States of America
- Branch: United States Navy/Department of Defense
- Era of Development: Late 20th century (1980s–1990s)
- Current Status: Active; currently in service with US Navy EOD, USSOCOM, and other DoD components
- Variants: MK 55 Mod 0, MK 55 Mod 1
Ordnance Class
- Type: Firing Device/Initiator
- Primary Role: Hand-held initiation of shock tube demolition systems
- Category: Mechanical percussion firing device
- Employment: Manually operated; used for controlled initiation of demolition charges, breaching operations, EOD render-safe procedures, and combat demolitions
Ordnance Family/Nomenclature
- Official US Navy Designation: Firing Device, Hand Held, MK 55 Mod 0 (single tube)
- Common Names: MK 55, Mark 55, Hand-Held Firing Device
- Related Family Members:
- MK 31 Firing Device: Earlier generation hand-held firing device
- MK 54 Mod 0: Dual-tube hand-held firing device (initiates two shock tubes simultaneously)
- MK 152 Mod 0 (RAMS): Remote Activation Munitions System for radio-controlled initiation
- NSN: 1375-01-375-5138 (MK 55 Mod 0)
- FSC: 1375 (Demolition Materials)
Nomenclature Distinction:
The MK 55 is a single-tube device, while the MK 54 is a dual-tube device. The dual-tube MK 54 allows simultaneous initiation of two separate shock tube lines from a single firing action, useful for redundant firing systems or multiple charge initiation.
Hazards
Primary Hazards:
- Mechanical Firing Hazard: Contains a spring-loaded striker and percussion element that can cause injury if fired improperly
- Initiation Risk: When connected to a shock tube system, will initiate the entire explosive train upon firing
- No Delay: Provides instantaneous initiation—user must ensure safe standoff before firing
Safety Considerations:
- Always verify all personnel are clear of the blast area before initiating
- Confirm shock tube connections are secure and routed properly
- Inspect device for damage before use
- Follow all applicable demolition safety procedures
Inherent Device Safety:
- Mechanical design—no electrical components to malfunction or cause accidental initiation from stray current or static
- Spring-loaded striker must be manually cocked and released
- Simple, robust construction minimizes failure modes
UXO Relevance:
The MK 55 itself is not typically encountered as UXO since it is an initiation device rather than an explosive. However, familiarity with the device is important for understanding modern demolition and breaching systems.
Key Identification Features
Physical Characteristics:
- Shape: Pen or pencil-shaped cylindrical device
- Size: Compact hand-held design, approximately 4–6 inches (100–150 mm) in length
- Weight: Lightweight, easily carried in a pocket or pouch
- Construction: Metal body with internal spring mechanism
External Features:
- Cylindrical Body: Contains the spring-loaded striker mechanism
- Shock Tube Receptacle: Opening or fitting to accept and secure shock tube
- Cocking Mechanism: Means to cock or arm the spring-loaded striker
- Trigger/Release: Mechanism to release the striker and fire the device
- Single Tube Design: Distinguishes it from the dual-tube MK 54
Markings:
- “MK 55 MOD 0” or “MK 55 MOD 1” designation
- US Navy/military markings
- NSN information
- Manufacturer identification
- Lot number and date of manufacture
Fuzing Mechanisms
Mechanism Type: Mechanical percussion hand-held initiator
Principal Components:
- Body/Housing: Cylindrical metal casing containing all components
- Spring-Loaded Striker: Compressed spring with attached striker pin
- Cocking Mechanism: System to compress and hold the spring in the armed position
- Trigger/Release Mechanism: Button, lever, or similar release to fire the striker
- Percussion Element: Primer or cap struck by the striker to produce initiation impulse
- Shock Tube Interface: Fitting to accept and properly align shock tube for initiation
Operating Principle:
The MK 55 operates as a hand-held percussion initiator for shock tube systems. Shock tube (also known as Nonel or non-electric tube) is a small-diameter plastic tube lined with a reactive material that propagates a low-energy signal at approximately 2,000 meters per second when initiated. The MK 55 provides the initial impulse to start this signal propagation.
Operating Sequence:
- Route shock tube from the demolition charge to the firing position
- Insert shock tube into the MK 55 receptacle and secure
- Ensure all personnel are in safe positions
- Cock the striker mechanism (compresses the spring)
- When ready to fire, actuate the trigger/release
- Striker impacts the percussion element, generating a flash
- Flash initiates the shock tube
- Signal travels through shock tube to initiate the blasting cap and main charge
Key Features:
- Non-Electric: Eliminates hazards from stray electrical current, radio frequency, and static electricity
- Instantaneous: No delay in signal transmission (shock tube signal travels at ~2,000 m/s)
- Reliable: Simple mechanical design with minimal failure modes
- Reusable Housing: The MK 55 body can be used with replacement initiator components
History of Development and Use
Background—Shock Tube Technology:
The development of shock tube (Nonel) technology in the 1970s revolutionized demolition and blasting operations by providing a non-electric alternative to traditional firing methods. Shock tube eliminated the risks associated with electrical initiation systems, including:
- Accidental initiation from stray electrical current
- Radio frequency interference (RFI) hazards
- Static electricity discharge
- Lightning strikes
Navy Development:
The US Navy developed a family of hand-held firing devices (MK 31, MK 54, MK 55) to provide reliable means of initiating shock tube systems in military applications. These devices were designed to meet the demanding requirements of:
- Explosive Ordnance Disposal (EOD): Safe initiation of render-safe and disposal charges
- Underwater Demolition/SEAL Teams: Combat demolitions in maritime environments
- Breaching Operations: Rapid initiation of door and wall breaching charges
- Special Operations: Reliable demolition capability in austere conditions
MK 55 Development:
The MK 55 Mod 0 was developed as a single-tube variant optimized for simplicity and weight savings. While the dual-tube MK 54 provides redundancy and multi-point initiation capability, many applications require only single-tube initiation, making the lighter, simpler MK 55 preferred.
Manufacturer Support:
Ensign-Bickford Aerospace & Defense (EBAD) produces Shock Tube Initiators (STI) designed to integrate with the MK 31, MK 54, and MK 55 firing devices, providing enhanced safety and reduced environmental contamination compared to earlier initiator designs.
Current Employment:
The MK 55 and related devices are currently used by:
- US Navy EOD units
- Naval Special Warfare (SEAL) teams
- US Army Special Forces
- MARSOC (Marine Raiders)
- Combat engineers
- Allied special operations forces
Evolution:
The MK 55 represents the maturation of hand-held shock tube initiation technology, building on lessons learned from the earlier MK 31 design. Continued development focuses on improved ergonomics, reliability, and integration with modern shock tube systems.
Technical Specifications
| Specification | Value |
|---|---|
| Designation | Firing Device, Hand Held, MK 55 Mod 0/Mod 1 |
| Type | Single-tube mechanical percussion initiator |
| NSN | 1375-01-375-5138 (Mod 0) |
| FSC | 1375 (Demolition Materials) |
| Size | Approximately 4–6 inches (100–150 mm) length |
| Weight | Lightweight (ounces) |
| Tubes | Single (1) |
| Initiation System | Shock tube (Nonel) |
| Power Source | None (mechanical) |
| Operating Temperature | Wide range; suitable for field conditions |
| Procurement | US Navy / DoD contracts |
Comparison with MK 54:
| Feature | MK 55 | MK 54 |
|---|---|---|
| Tubes | Single (1) | Dual (2) |
| Weight | Lighter | Heavier |
| Redundancy | No | Yes (two independent tubes) |
| Application | Single charge/line | Redundant firing / dual initiation |
| NSN | 1375-01-375-5138 | 1375-01-377-8032 |
Frequently Asked Questions
Q: What is the difference between the MK 55 and MK 54 firing devices?
A: The primary difference is the number of shock tubes each can initiate. The MK 55 is a single-tube device, while the MK 54 is a dual-tube device capable of simultaneously initiating two shock tube lines. The MK 54 is preferred when redundancy is required or when two separate charges must fire together, while the MK 55 is lighter and simpler for single-charge applications.
Q: What is shock tube and why is it used with the MK 55?
A: Shock tube (also known as Nonel) is a small-diameter plastic tube with a thin reactive coating on its inner surface. When initiated, it propagates a low-energy detonation signal at approximately 2,000 meters per second to initiate blasting caps and charges. Shock tube systems are preferred for military demolition because they are immune to accidental initiation from stray electricity, radio frequencies, and static discharge—making them safer than electric detonators in combat environments.
Q: Who uses the MK 55 firing device?
A: The MK 55 is used primarily by US Navy EOD units, Naval Special Warfare (SEAL teams), US Army Special Forces, MARSOC, combat engineers, and allied special operations forces. It is a standard component of modern military demolition systems wherever shock tube initiation is employed.
Q: Is the MK 55 reusable?
A: The MK 55 housing/body is designed for repeated use. However, the internal percussion element or initiator component is consumed with each firing and must be replaced. Replacement Shock Tube Initiators (STI) are available to reload the device for subsequent use.
Q: What advantages does mechanical initiation have over electrical firing systems?
A: Mechanical percussion initiation eliminates several hazards associated with electrical systems: (1) no risk from stray electrical current, (2) immunity to radio frequency interference (RFI), (3) no static electricity hazards, and (4) no battery or power source required. This makes the MK 55 ideal for operations in electromagnetically contested environments or where electrical hazards are present.
Q: How does the MK 55 relate to the MK 31 firing device?
A: The MK 31 is an earlier-generation hand-held firing device that preceded the MK 54 and MK 55. The MK 55 represents an evolution in design with improved ergonomics and reliability. EBAD Shock Tube Initiators are designed to integrate with all three devices (MK 31, MK 54, and MK 55).
Q: Can the MK 55 be used underwater?
A: Shock tube systems, including compatible firing devices, can be used in underwater demolition applications. However, specific waterproofing requirements and depth limitations depend on the particular shock tube and initiator components used. Naval Special Warfare applications specifically require underwater-capable initiation systems.
Q: What training is required to use the MK 55?
A: Use of the MK 55 and shock tube demolition systems requires formal military demolition training. Navy EOD, Special Forces, SEAL, and combat engineer courses include instruction on non-electric initiation systems. Unauthorized or untrained use of demolition equipment is dangerous and illegal.
Safety Notice
All demolition equipment, including firing devices, should only be used by trained and authorized military or law enforcement personnel. The MK 55 and associated shock tube systems are designed to initiate explosive charges and can cause death or serious injury if misused. Never attempt to use, modify, or experiment with military demolition equipment. This lesson is provided for educational and identification training purposes only. If you encounter military demolition materials, do not touch them—contact military or law enforcement authorities immediately.