HMMWV Safety Improvements

The commitment of U.S. forces to Iraq and Afghanistan included the shipment of thousands of vehicles to the theater of operations, most of them HMMWVs. As of October 2007, approximately seventy percent of land transport vehicles in Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF) were HMMWVs, which accounted for half of all fatal land transport accidents in these deployments. HMMWV accidents were studied by safety specialists and efforts began to protect HMMWV occupants from the effects of common accident scenarios. HMMWV modifications were designed to decrease the number of injuries that occur while operating the vehicle. As new HMMWVs were produced, the enhanced safety features were factory installed. For HMMWVs already in the field, the same safety enhancements were ordered installed in theater, for example by the Combatant Forces Land Component Commander in Kuwait.

M1114 HMMWV rear seat occupant is exposed to risks without proper seat belts.  In addition, the design of the seat forces his knees to be higher than his hips, a position that can cause back injury by decreasing the lumbar curve and the spine's ability to absorb shock while the vehicle is in motion, a problem to be eliminated in future seat design and procurement
M1114 HMMWV rear seat occupant is exposed to risks without proper seat belts. In addition, the design of the seat forces his knees to be higher than his hips, a position that can cause back injury by decreasing the lumbar curve and the spine's ability to absorb shock while the vehicle is in motion, a problem to be eliminated in future seat design and procurement.

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HMMWV Safety Improvements

HMMWV accident scene:  rollover into water
HMMWV accident scene: rollover into water.

In the early 2000s, the three leading types of military land transport accident types were:

  • Vehicle overturned
  • Vehicle ran off the road
  • Collision with another vehicle

About two-thirds of all fatal land transport military vehicle incidents in OIF/OEF involved vehicles that either overturned or ran off the road. The three accident types accounted for 90 percent of the incidents and 91 percent of fatalities. Just over half of vehicles involved in fatal incidents were a type of HMMWV. For actual cause of death, drowning was the leading factor, followed by crushing.

Analysis of HMMWV accidents yielded insights that suggested vehicle enhancements for HMMWV safety. In early 2005, the Army began fielding enhancements, applied to combat zone vehicles first, installed in all eligible HMMWVs worldwide in the following years, primarily the Up-Armored HMMWV (UAH) models M1114 and M1151. Other enhancements followed after more development. The enhancements include:

  • Occupant Seatbelts
  • Gunner Restraint System
  • Improved Vehicular Intercom System (AN/VIC-3)
  • Automatic Fire Extinguishing System (AFES)
  • Vehicle Emergency Escape (VEE) Windows
  • Single Movement Combat Lock
  • Crew Extraction Equipment

In addition to improvements to the vehicle iself, the HMMWV Egress Assistance Trainer (HEAT) was developed and deployed for realistic training of Soldiers and Marines for roll-over accidents. By 2007, training in the use of the new safety equipment and related procedures became mandatory for all Army and Marine Corps personnel deploying to Afghanistan or Iraq.

Each of these topics is further described in the following sections.

HMMWV improved seat belt system
HMMWV improved seat belt system.

Occupant Seatbelts

HMMWV fatalities were much higher where Soldiers were not wearing seatbelts. In one evaluation for OIF/OEF, the risk of a fatal injury in a HMMWV accident was six times greater for Soldiers not wearing seatbelts than for those who were. Seatbelts were not originally provided for all positions in the HMMWV and those that had belts were the less effective lap belt design. Furthermore, interviews revealed that body armor, rucks or other equipment often were too bulky for seatbelts to pass around. The first lap and shoulder belt design, while an improvement, tended to get stuck on body armor plates.

Starting in early 2006, new seatbelts were provided for the HMMWV in a three point design, with a faster release, more reliable latching mechanism, and greater length for use while wearing personal protective equipment and combat loads. The new straps form a Vee with the lap and shoulder sections, with two buckles that release separately and both upper and lower webbing retractors. The NSN for Parts Kit, Seat Belt is 2540-01-542-5419 for the M1114. Click on this link for a M1114 seatbelt diagram and parts list (811KB PDF).


Gunner Restraint System (GRS)
Gunner Restraint System (GRS).

Gunner Restraint System

The Gunner Restraint System (GRS) is designed to prevent the Up-Armored HMMWV (UAH) turret gunner from being ejected in a crash or rollover. It also provides stabilization during high speed maneuvers and operations on rough terrain. The GRS consists of a five-point harness attached to a locking mechanism located inside the vehicle. The restraint system easily locks into place while allowing the gunner freedom of movement and the necessary protection to keep him in the turret.

The early version of the M1114 Gunner Restraint System was found to be troublesome. Improvements incorporate a swivel to allow greater mobility in the turret without twisting the straps, a quick release for rapid egress, and adjustable tail straps to accommodate the gunner's height. These solutions are incorporated in the retrofit kits identified by NSN 2540-01-542-7412 for the M1114 and NSN 2540-01-542-1130 for the M1151. The two kits differ by a support bar that connects to the restraint harness assembly. (Note: NSN 4240-01-542-8160 is the harness alone. Click for Gunner Restraint System parts layout.)

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AN/VIC-3 installed in a HMMWV
AN/VIC-3 installed in a HMMWV.

Improved Vehicular Intercom System

The interior of a HMMWV is a high noise environment, made worse by overland travel or combat operations. The original AN/VIC-1 vehicle intercom used in the HMMWV was limited to a three man configuration. To enhance communication between the gunners in the rear or turret of the vehicle and all the vehicle occupants, the HMMWV intercom was upgraded to the AN/VIC-3 in a five man configuration, a system specifically designed for ground combat vehicles. An intercom at each crew member station supports communication between and among the crew and enables monitoring of radio voice communication.

The AN/VIC-3 is compatible with the Improved Tactical Headset designed to protect Soldiers' hearing and to allow them to communicate in the high-noise environment of the M1114 UAH. Designed to fit under the standard Personnel Armor System Ground Troops (PASGT) Kevlar helmet and the newer Advanced Combat Helmet (ACH), the ITH provides hearing protection through both active and passive noise reduction technologies and enables Soldiers or Marines to communicate in the high-noise environment (up to 95-plus decibels) typical of the M1114 UAH. More information is available in TM 11-5830-263-10 Operators Manual for Vehicular Intercommunication Set AN/VIC-3.


Components of the Automatic Fire Extinguishing System in a HMMWV
Components of the Automatic Fire Extinguishing System in a HMMWV.

Automatic Fire Extinguishing System (AFES)

The HMMWV Automatic Fire Extinguishing System (AFES) provides enhanced survivability protection against improvised explosive devices (IED) and other combat fire threats to the occupants of the vehicle. The HMMEV AFES is based on similar systems used in armored vehicles. AFES is supplied as a retrofit kit composed of fire sensors and extinguishers that react in milliseconds to automatically detect heat or light and then suppress explosive fires.

Delivery of the retrofit kits began in 2005 with over 12,500 units expected to be installed in combat zones in M1114 and M1152 UAH vehicles. This equipment is also called the HMMWV Fire-Suppression System (FSS).


Demonstration of Vehicle Emergency Escape (VEE) window.  Photo:  BAE Systems.
Demonstration of Vehicle Emergency Escape (VEE) window. Photo: BAE Systems.

Vehicle Emergency Escape (VEE) Windows

The UAH can trap its occupants if the doors become inoperable in an accident situation. Vehicle Emergency Escape (VEE) window kits allow Soldiers inside the vehicle to remove the windshield of the HMMWV in seconds in order to exit the vehicle in an emergency. A three-step process enables crew members exit the vehicle through the window opening after:

  • Pulling the locking pins
  • Rotating the latch handles
  • Pushing the window out

Single Movement Combat Lock on HMMWV door
Single Movement Combat Lock on HMMWV door.

Single Movement Combat Lock

The M1114 is equipped with heavy door locks to protect the crew from unauthorized entry and to prevent doors from coming open in the event of an accident, mine strike or IED explosion. This benefit has the potential downside of making it difficult to escape from the HMMWV or barring access by rescue personnel.

In addition to the VEE Windows, improved HMMWV lock systems make it easier to get out of the vehicle, especially in water. The Single Movement Combat Lock provides crews with a robust door locking mechanism that can be quickly opened using one hand during emergency egress situations. They are less likely to jam in an accident or explosion incident. The previous design had two separate devices and two hands were needed to unlock and open the door.


Demonstration of the Emergency Rescue Wrench
Demonstration of the Emergency Rescue Wrench.

Crew Extraction Equipment

In case the crew inside is incapacitated and cannot escape on their own, the Emergency Rescue Wrench (ERW, manufactured by O'Gara-Hess & Eisenhardt, Armor Holdings Company) is an emergency ingress tool for M1114 HMMWVs, similar in look to an X-shaped wheel wrench. The ERW is mounted outside the crew compartment, ready to be used to remove bolts that release the doors, allowing the door to be pryed off the vehicle.

In the aftermath of an accident or attack, when it is impractical to use the Emergency Rescue Wrench, the Crew Extraction Device is available, one installed on each door. Rescue teams, or anyone at the scene, will be able to attach a tow strap or chain to the HMMWV door exterior to forcibly remove the door from the HMMWV, avoiding the need to remove bolts. Before, bolts had to be unscrewed to pry off the doors. The Crew Extraction Device went into production in June 2006.


HMMWV Egress Assistance Trainer (HEAT)

HMMWV Egress Assistance Trainer (HEAT)
HMMWV Egress Assistance Trainer (HEAT).

In response to the high number of rollover events, the HMMWV Egress Assistance Trainer (HEAT) was developed to train Soldiers and Marines to safely escape from an overturned vehicle and to reinforce safety measures such as proper seatbelt use. The HMMWV Egress Trainer is a box-like training device resembling a humvee that allows occupants to gain experience in properly escaping during an emergency. It is capable of rolling several times a minute and stopping at varying angles.

To add to the training reality and impact, the HEAT is loaded with assorted loose items that will be thrown around inside while sounds of simulated gunfire are heard from outside the vehicle. The qualification standard is to be able to get out of an inverted HMMWV in 20 seconds. Worldwide use of HEAT started in 2007 at Army and USMC bases.

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