The GMV is a modified HMMWV that has been adapted for special operations use, mostly based on lessons learnt during Operation Desert Storm in 1991.
Several variants, tailored to different special operations units, exist:

GMV-S (Special Forces)GMV-R (75th Ranger Regiment)
GMV-N (Navy SEALs)

The GMV has the following features:

heavier suspension
more rugged tires
improved ground clearance
more powerful engine
open bed for improved storage/access
winch for towing other vehicles (up to 4,200 pounds)
GPS navigation system

GMVs feature a set of mounts onto which various weapons can be fitted. These include:

M2 .50 machine guns
M240 7.62mm belt-fed machine guns
MK19/MK47 40mm grenade launchers
M249 SAW 5.56mm machine guns

GMVs can be fitted with smoke grenade launchers, rear and front. These tubes launch smoke canisters which airburst above and around the GMV, creating an instant smoke screen - very useful when breaking contact.
The GMV has a cruising range of up to 275 miles and ODA GMV teams may well need to operate far behind enemy lines, on their own, with only occasional re-supply from the air. Special Forces ODAs undergo extensive training in driving and maintaining the GMVs, with an emphasis on off-road handling and in-field repairs.

GMVs feature an open rear, where an enclose cabin would normally be. This flat bed area is used to store all the fuel, ammunition, rations and other supplies that the ODA’s mission requires.
Early models of the GMV were based around the HMMWV M1025 chasis. Later models of GMVs included versions based on the M1113 HMMWV chasis. Another model, this time based on the M1165 HMMWV, can be fiited with armor kits to create an ‘up-armored’ GMV with additional armor plating and an optional ballistic shield around the top gunner’s turret.