The United States Marine Corps, like the other branches of the armed services, has specific requirements for their body armor. In the case of the Marines, the standards apply to both the MLE (armament adjustment device) and the PT (personnel carrying armor). For the Air Force the standard is the USSAS (Universal Service Uniform) but for the Navy the standards apply only to the rear end of the boats, destroyers, aircraft, and some police vehicles. The Marine Corps currently has only one piece of armor designated as MLE (man-made steel) that is used for both assault rifles and body armor for personnel inside the vehicle. Because of this the other armor used by the Marine Corps is classified as soft armor.
Soft armor is also used in less common applications such as bullet resistant vests and load bearing shields. These are used where the armor will be in direct contact with the gun, usually for the front plate or the back plate. Although it is generally categorized as soft armor, the best examples of this type of armor are the soft plates used by the vest worn by the Navy Seals, and the heavy plate carriers used by the Army. Hard armor is generally used on the ends of rifles, on shotguns, and on handgun magazines. Although it is generally classified as hard armor, the best examples of this type of armor are the soft plates used by the Navy Seals and the heavy plate carriers used by the Army.
Both MLE and PT armor are available in rifle bullet resistant vests that can be fitted on the end of the rifle. These plates have larger amounts of steel and Kevlar, compared to the soft armor plates. MLE plates must be welded to a steel core whilePT plate carriers must be made out of fiberglass and Kevlar. Other examples of hard armor include the shotgun vests and the vehicle armor that is commonly used by the Guard and Air Force personnel. Since the US Army and the US Navy still prefer soft armor for rifles, there is a limit to the amount of hard armor that can be installed on an MRE or PT.