For many years, both the Army and Marine Corps vehicles and equipment used only MIL-PRF-2104 (it used to be MIL-L-2104) in the engine, transmission, some hydraulic systems,and in some cases manual transmissions. In effect, this oil was and is a multifunctional engine/transmsission oil. That was used everywhere except in the cold regions like Alaska and other cold regions where they reverted to their Arctic Engine Oil, MIL-PRF-46167. When vehicles are placed in temporary storage or prepositioning, they use an oil that is both a preservative as well as an operational oil and that is MIL-PRF-21260. A few years ago, there were two additional semicommercial specifications developed called Commercial Item Descriptions and these cover the engine oils for the administrative vehicles, but all tactical items are required to use the military specification products. All the gas turbine items (namely the Abrams tanks and some power generation items) use a polyol ester that is defined by MIL-PRF-23699 which is the oil that the Navy uses in their aircraft.
All these military specifications have qualification product listings which lists each company's approved product that has successfully passed all the engine and other associated testing. Once qualified, the formulation in fixed so the supplier can't do a quick switch. When solicitations are sent out for companies to bid on, only products that have been approved can be considered. But the one catch (as with all government procurement) is that the contracts are awarded on the lowest bidder. Therein lies the problem.
Several of the above military specifications allow the use of re-refined basestocks. But, all the same performance requirements have to be met regardless of the type of basestocks that are used. Those products that are approved regardless of what basestocks are used have to meet all the minimium requirements.
