In 1979, the military announced a competition for the design of a new vehicle and released preliminary specifications. At the beginning of 1981, the Army released the final specifications for the new vehicle called the High Mobility Multipurpose Wheeled Vehicle, HMMWV. The specifications would allow the HMMWV to replace several vehicles in the current inventory while providing capabilities beyond any other vehicle.
The specs gave requirements for both the shape and mechanics of the vehicle. Roof height, hood height, and profile were defined. Furthermore, the military wanted to standardize mobility for combat vehicles so that all could remain together. Therefore, the HMMWV had to meet the same specs as the Bradley's and M1 tanks. The 16" ground clearance, 60% grade, 40% side slope, 18" vertical step, 30" fording w/o preparation, etc. are the military's mobility requirements for combat vehicles, including the HMMWV.
Civilian HUMMER
Sometimes people call the military HMMWVs as HUMMERs or vice versa. Technically this is wrong. The military HMMWVs are called "Hum-Vees". The commercial (a.k.a. civilian) models are called HUMMERs. While they are closely related, there are differences between the families.