When becoming aware of the U.S. Army's desire for a versatile new light weapons carrier/reconnaissance vehicle, as early as 1969 FMC Corporation started development on their XR311 prototype and offered it for testing in 1970.

Adjusting to Congress's expectations, the Army increased the scale of the program, then called the XM966 High Mobility Weapons Carrier (CSVP), to replace multiple other trucks.

The specifications called for a diesel engine,[23] excellent on and off-road performance, the ability to carry a large payload, and improved survivability against indirect fire.

Yakima Training Center, Washington, was the main testing grounds for HMMWVs from 1985 through December 1991, when the motorized concept was abandoned and the division inactivated.

However, the chassis survivability allowed the majority of those crews to return to safety, though the HMMWV was never designed to offer protection against intense small arms fire, much less machine guns and rocket-propelled grenades.

With the increase in direct attacks and asymmetric warfare in Iraq, AM General diverted the majority of its manufacturing power to producing these vehicles.

Some soldiers would remove features from Humvees, including what little armor it had and sometimes even entire doors, to make them lighter and more maneuverable for off-road conditions and to increase visibility.

Although this somewhat improved survivability, bolting on armor made the Humvee an "ungainly beast", increasing weight and putting a strain on the chassis, which led to unreliability.

However, deploying the vehicle to conflict zones where it was exposed to a full spectrum of threat which it was neither designed to operate, or be survivable in, led to adding protection at the cost of mobility and payload.

[8] On 22 April 2022, Pentagon Press Secretary John F. Kirby described a package of military equipment being transported to Ukraine to assist in its war with Russia, including "100 armored Humvee vehicles".

As the role of American forces in Iraq changed from fighting the Iraqi Army to suppressing the insurgency, more armor kits were being manufactured, though perhaps not as fast as production facilities were capable.

[47] Another drawback of the up-armored HMMWVs occurs during an accident or attack, when the heavily armored doors tend to jam shut, trapping the troops inside.

[51] In addition, Vehicle Emergency Escape (VEE) windows, developed by BAE Systems, were fielded for use on the M1114 up-armored HMMWV, with 1,000 kits ordered.

Additionally, some HMMWVs have been fitted with a remotely operated CROWS weapon station, which slaves the machine gun to controls in the back seat so it can be fired without exposing the crew.

Another weakness for the HMMWV has proven to be its size, which limited its deployment in Afghanistan because it is too wide for the smallest roads and too large for many forms of air transport compared to jeeps or Land Rover-sized vehicles (which are, respectively, 24 and 15 inches narrower).

The short-term replacement efforts utilized commercial off-the-shelf vehicles as part of the Mine Resistant Ambush Protected (MRAP) program.

[60] The U.S. Marine Corps issued a request for proposals in 2013 for its Humvee sustainment modification initiative to upgrade 6,700 expanded capacity vehicles (ECVs).

Key areas of improvement include upgrades to the suspension to reduce the amount of force transferred to the chassis, upgrading the engine and transmission for better fuel efficiency, enhancements to the cooling system to prevent overheating, a central tire inflation system to improve off-road mobility and ride quality, and increased underbody survivability.

[63] Northrop Grumman developed a new chassis and powertrain for the Humvee that would combine the mobility and payload capabilities of original vehicle variants while maintaining the protection levels of up-armored versions.

Although the SCTV costs more at $200,000 per vehicle, the company claims it can restore the Humvee for operational use, combining Humvee-level mobility and transportability with MRAP-level underbody protection as a transitional solution until the JLTV is introduced in significant numbers.

[8] Although the Army plans to buy 49,100 JLTVs and the Marine Corps 5,500, they are not a one-for-one replacement for the Humvee, and both services will still be left operating large fleets.

It has all-wheel drive with an independent suspension and helical gear-reduction hubs similar to portal axles which attach towards the top rather than the center of each wheel to allow the drivetrain shafts to be raised for 16 in (410 mm) ground clearance.

In combat conditions, the HMMWV can be delivered by the Low Altitude Parachute Extraction System which pulls the vehicle out of the open rear ramp just above the ground without the aircraft having to land.

The M1114 meets Army requirements for a scout, military police, and explosive ordnance disposal vehicle with improved ballistic protection levels.

[78] The M1116 features an expanded cargo area, armored housing for the turret gunner, and increased interior heating and air conditioning system.

The vehicle features a monocoque V-shaped hull and angled sides to help deflect rocket-propelled grenades (RPGs) with scalable levels of protection.

Also included are a powerful air conditioner and heating system, run-flat tires, a thermal guard liner under the roof, sharp edges removed from inside the cabin, blast attenuating seats, and a folding gunner's turret allowing rapid deployment from a cargo aircraft or shipboard below deck.

The upgrade can enhance the survivability of previously soft-skinned versions, sometimes sold by the U.S. as Excess Defense Articles, while costing and weighing less than a comparable MRAP.

[179][180] In Australia, a Gold Coast-based company called Rhino Buggies produces replicas of the Hummer H1 based on the Nissan Patrol 4WD vehicle for around A$30,000.

[181] In the U.S., four companies offered Hummer-look-alike body kits that can be mated to GM full-size trucks and Suburban chassis and, in some cases, Ford, Dodge, and Cadillac applications.