BLU-91/B Anti-Tank Mine Submunition
1. Overview
The BLU-91/B is an air-delivered, scatterable anti-tank mine submunition designed for rapid area denial against armored vehicles. Developed as part of the United States GATOR mine system, the BLU-91/B represents a significant advancement in air-delivered mine warfare, allowing aircraft to rapidly emplace minefields without ground forces. The munition combines a magnetically-influenced fuze with a self-destruct feature, making it one of the first “smart” scatterable mines designed to reduce long-term UXO hazards.
2. Country/Bloc of Origin
- Country: United States of America
- Developer: Honeywell Defense and Marine Systems (later Alliant Techsystems)
- Development Period: Late 1970s to early 1980s
- Service Entry: 1983
- International Users: Primarily US forces; limited export to close NATO allies
The BLU-91/B was developed in response to Cold War requirements for rapidly deployable anti-armor barriers against Warsaw Pact armored formations in Central Europe. The mine was designed to meet both tactical effectiveness requirements and emerging concerns about persistent landmine hazards.
3. Ordnance Class
| Attribute | Classification |
|---|---|
| Type | Submunition / Scatterable Mine |
| Role | Anti-Tank (AT) |
| Delivery Method | Air-delivered via dispenser (CBU-78/B, CBU-89/B GATOR) |
| Category | Area Denial Munition |
| Mine Type | Off-route / Belly Attack |
The BLU-91/B is classified as a scatterable anti-tank mine under international conventions. It is designed to attack the relatively thin bottom armor of tanks and armored vehicles as they pass over or near the mine.
4. Ordnance Family / Nomenclature
Primary Designation:
- BLU-91/B (Bomb Live Unit)
Parent Systems:
- CBU-78/B GATOR – Navy/Marine Corps variant containing 45 BLU-91/B and 15 BLU-92/B mines
- CBU-89/B GATOR – Air Force variant containing 72 BLU-91/B and 22 BLU-92/B mines
Related Munitions:
- BLU-92/B – Companion anti-personnel mine in the GATOR system
- M75 – Similar ground-delivered anti-tank scatterable mine (ADAM system)
NATO Stock Number (NSN): 1345-01-138-8649
Common Names:
- GATOR AT Mine
- Gator Anti-Tank Submunition
5. Hazards
Primary Hazards
| Hazard Type | Description |
|---|---|
| Blast | Main charge detonation creates significant overpressure |
| Fragmentation | Case fragments generated upon detonation |
| Penetration | Shaped charge/EFP effect against vehicle undersides |
Sensitivity Factors
- Magnetic Influence: Primary triggering mechanism – highly sensitive to ferrous metal mass
- Tilt Sensitivity: Anti-disturbance feature activates on significant movement
- Self-Destruct: Mines have battery-powered self-destruct timers (variable settings)
- Low Battery Hazard: Mines with depleted batteries may fail to self-destruct, becoming persistent UXO
Safety Considerations
- Arming Delay: Mines have a brief arming delay after dispensing to allow aircraft escape
- Random Arming Times: Individual mines arm at slightly different times to prevent systematic clearing
- Anti-Handling: Tilt-sensitive fuze functions as anti-handling device
- UXO Risk: Dud rate and self-destruct failures create significant post-conflict hazards
Kill/Damage Radius
- Vehicle Kill: Direct attack on passing armored vehicles
- Damage Area: Blast and fragmentation hazardous within approximately 10 meters
- Danger Zone: Minimum safe distance for unprotected personnel is 50 meters from functioning mine
⚠️ WARNING: The BLU-91/B contains a magnetically-influenced fuze that will detonate in the presence of large ferrous metal objects. All ordnance should be considered armed and dangerous. Never approach suspected BLU-91/B munitions without proper EOD training and equipment.
6. Key Identification Features
Physical Characteristics
| Dimension | Measurement |
|---|---|
| Length | Approximately 13 cm (5.1 inches) |
| Width | Approximately 7 cm (2.8 inches) |
| Height | Approximately 5 cm (2.0 inches) |
| Weight | Approximately 1.7 kg (3.75 lbs) |
Visual Identification
- Shape: Rectangular/box-shaped with slightly rounded edges
- Color: Olive drab (OD) green body
- Markings: Yellow stenciled text indicating “MINE, AT” with lot numbers and manufacturer data
- Material: Predominantly plastic (non-metallic) case to reduce detectability
- Distinctive Features:
- Small stabilizing ribbon/drogue may be attached or nearby
- Magnetic sensor visible as small protrusion
- Four spring-loaded metal legs deploy after landing to provide standoff
Post-Deployment Appearance
After deployment, the BLU-91/B rests on the ground supported by four spring-loaded legs that deploy upon landing. These legs provide the necessary standoff distance for the warhead to function effectively against vehicle undersides. The stabilization ribbon may be found nearby or still attached.
Condition Indicators
- Armed: Legs deployed, resting on ground
- Partially Functioned: Damaged casing, possible leg deployment failure
- Dud/UXO: May appear intact but failed to function; extremely dangerous
7. Fuzing Mechanisms
Primary Fuze System
The BLU-91/B employs a magnetically-influenced fuze as its primary triggering mechanism:
| Component | Function |
|---|---|
| Magnetic Sensor | Detects disturbance in local magnetic field caused by passing ferrous metal (vehicle) |
| Signal Processor | Analyzes magnetic signature to distinguish vehicles from other metal objects |
| Firing Circuit | Initiates detonation when valid target signature detected |
Arming Sequence
- Dispensing: Mine is ejected from dispenser canister
- Stabilization: Drogue/ribbon deploys to orient mine during descent
- Landing: Impact triggers leg deployment mechanism
- Arming Delay: Electronic timer counts down arming delay period
- Armed State: Mine becomes active and sensitive to magnetic influence
Safety Mechanisms
- Arming Delay: Prevents detonation during and immediately after dispensing
- Setback Safety: Requires acceleration of dispensing to initiate arming sequence
- All-Ways Acting: Mine functions regardless of landing orientation (within limits)
Self-Destruct System
The BLU-91/B incorporates a battery-powered self-destruct mechanism:
- Timer Options: Multiple self-destruct time settings (hours to days)
- Function: After preset time expires, mine self-destructs
- Reliability Issue: Battery depletion before timer expiration can cause self-destruct failure
- Self-Deactivation: If self-destruct fails, mines may self-deactivate (become inert) but this is not guaranteed
Anti-Handling Features
- Tilt Sensor: Mine detonates if significantly disturbed or moved after arming
- Purpose: Prevents manual clearance of minefield; protects mine from tampering
8. History of Development and Use
Development Background
The BLU-91/B was developed during the late Cold War period in response to NATO’s need for rapidly deployable anti-armor barriers. The threat of massive Warsaw Pact armored formations advancing through the Fulda Gap and other potential invasion routes in Central Europe drove requirements for air-delivered mining capability.
Development Timeline
| Year | Event |
|---|---|
| Late 1970s | Development initiated by Honeywell |
| Early 1980s | Testing and evaluation completed |
| 1983 | Entered service with US Air Force and Navy |
| 1991 | Combat debut in Operation Desert Storm |
| 2000s | Continued service despite cluster munition concerns |
Combat Employment
Operation Desert Storm (1991): The GATOR system saw its combat debut during the Gulf War. US aircraft employed CBU-89/B dispensers to emplace minefields across Iraqi lines of communication and potential avenues of approach. The mines were credited with disrupting Iraqi armored movements and channeling forces into kill zones.
Kosovo (1999): Limited use reported during NATO air operations.
Controversy and Restrictions
The BLU-91/B has been subject to significant international scrutiny:
- 2008 Convention on Cluster Munitions: Banned by many nations (US did not sign)
- Ottawa Treaty: While primarily addressing anti-personnel mines, related discussions affected scatterable AT mine policy
- US Policy Changes: Various policy restrictions on use and export implemented over time
Current Status
The BLU-91/B remains in US inventory but faces restrictions on use. The US military has moved toward alternative systems and precision-guided munitions. Existing stocks are subject to ongoing policy review regarding cluster munitions.
9. Technical Specifications
Explosive Content
| Specification | Detail |
|---|---|
| Main Charge Type | Composition B or similar high explosive |
| Charge Weight | Approximately 0.57 kg (1.26 lbs) |
| Warhead Type | Self-Forging Fragment (SFF) / Explosively Formed Penetrator (EFP) |
Performance Characteristics
| Specification | Detail |
|---|---|
| Armor Penetration | Capable of penetrating bottom armor of most main battle tanks |
| Activation Range | Magnetic sensor effective within approximately 1-2 meters of passing vehicle |
| Operating Temperature | -40°C to +52°C (-40°F to +126°F) |
| Self-Destruct Time | Variable (typically 4 hours to 15 days, depending on setting) |
Dispenser Configuration
| System | BLU-91/B Quantity | BLU-92/B Quantity |
|---|---|---|
| CBU-78/B | 45 | 15 |
| CBU-89/B | 72 | 22 |
Battery and Electronics
- Power Source: Lithium battery
- Battery Life: Limited; determines maximum self-destruct time reliability
- Environmental Sealing: Waterproof to operational depth requirements
10. Frequently Asked Questions
Q: What is the relationship between the BLU-91/B and BLU-92/B? A: The BLU-91/B (anti-tank) and BLU-92/B (anti-personnel) are companion submunitions in the GATOR mine system. They are dispensed together from CBU-78/B and CBU-89/B cluster bombs to create mixed minefields. The anti-personnel mines protect the anti-tank mines from dismounted clearance attempts, while the anti-tank mines engage armored vehicles. This combined approach creates a more effective area denial barrier than either mine type alone.
Q: How does the magnetic influence fuze distinguish between a tank and other metal objects? A: The BLU-91/B’s magnetic sensor detects disturbances in the local magnetic field caused by large ferrous metal masses. The signal processor analyzes the magnetic signature’s characteristics—including its strength, duration, and pattern—to distinguish armored vehicles from smaller metal objects. However, this system is not perfect; large metal objects like heavy trucks or construction equipment may also trigger the mine, and some modern vehicles with reduced magnetic signatures may be harder to detect.
Q: Why does the BLU-91/B have spring-loaded legs? A: The four spring-loaded legs serve a critical tactical function. When deployed, they elevate the mine’s warhead to a specific standoff distance above the ground. This standoff is essential for the self-forging fragment (SFF) or explosively formed penetrator (EFP) warhead to properly form and achieve maximum armor penetration against the thin bottom armor of vehicles passing overhead. Without proper standoff, the warhead’s effectiveness would be significantly reduced.
Q: What happens if the self-destruct mechanism fails? A: Self-destruct failure is a significant concern with the BLU-91/B. If the battery depletes before the self-destruct timer expires, or if a mechanical/electronic failure occurs, the mine may remain armed and dangerous indefinitely, becoming persistent UXO. While a secondary self-deactivation feature may eventually render the mine inert through battery depletion of the firing circuit, this is not guaranteed. Failed self-destruct is one of the primary reasons cluster munitions containing such mines have faced international criticism and restrictions.
Q: Can the BLU-91/B be safely cleared by manual means? A: No. The BLU-91/B incorporates a tilt-sensitive anti-handling fuze that will detonate the mine if it is significantly disturbed after arming. This feature is specifically designed to prevent manual clearance. EOD personnel must use remote or standoff methods to neutralize these mines. Any suspected BLU-91/B should be treated as armed and extremely dangerous, with a wide cordon established until qualified EOD personnel can respond.
Q: How effective is the BLU-91/B against modern armored vehicles? A: The BLU-91/B’s EFP warhead was designed to defeat the bottom armor of main battle tanks from the Cold War era, which is typically thinner than frontal or turret armor. Against modern main battle tanks, effectiveness varies depending on any additional belly armor or mine-resistant modifications. The mine remains highly effective against lighter armored vehicles, infantry fighting vehicles, and armored personnel carriers, which generally have less protection against belly attacks.
Q: Is the BLU-91/B considered a “cluster munition” under international law? A: Yes. The BLU-91/B is a submunition dispensed from cluster munition dispensers (CBU-78/B and CBU-89/B), making the complete weapon system a cluster munition under the 2008 Convention on Cluster Munitions (CCM). Nations that have ratified the CCM are prohibited from using, producing, stockpiling, or transferring cluster munitions including the GATOR system. The United States has not signed the CCM and retains these weapons in its inventory, though subject to national policy restrictions.
Q: What makes unexploded BLU-91/B submunitions particularly dangerous for post-conflict clearance? A: Several factors make BLU-91/B UXO especially hazardous: the magnetic influence fuze may arm even if the mine didn’t function as intended; the anti-handling tilt fuze makes any movement potentially fatal; the plastic construction makes detection difficult; mines may be partially buried or obscured by vegetation; and battery degradation creates unpredictable behavior. Additionally, clearance personnel may be working in mixed minefields containing both BLU-91/B anti-tank and BLU-92/B anti-personnel mines, requiring simultaneous attention to multiple threat types.
This document is for educational and training purposes only. All ordnance should be treated as dangerous until rendered safe by qualified EOD personnel. Never attempt to handle, move, or disturb any suspected explosive ordnance.