Back in the 1970's, the Department of Defense became concerned that too many people were developing Operating Systems and Programming Languages that were incompatible with each other. Because the military feared this would lead to confusion (particularly in dispensing lucrative military contracts for software), the DOD declared that all software purchased by any military organization must use the higher-order programming language ADA (named after Ada Lovelace, mistress of Charles Babbage, inventor of an early mechanical calculator). Initially, a few companies (that are no longer around) got onboard and developed some mainframe platforms that used the ADA environment and the ADA language requirement became is MIL-SPEC (a standard to which everything the military buys must adhere).
Fast forward to 1990, where the military, like every other organization in the world, was dying to to get PCs into the office. The problems was, companies like Microsoft and Apple had no interest in ADA. They developed their own, far superior, OS' and software that didn't bother with ADA or the MIL-SPEC. No ADA software was ever created that could run a PC.
So, the DOD, in it's infinite wisdom, said, "OK, you can buy PC's and software off of a government contract, but only the brands we say BUT, you will need a approved waiver for to purchase non MIL-SPEC". So, whole departments were created simply to process waivers for military units to buy PC.
The moral of this story is ... when they need to, the military will go around their own rules to buy whatever they need in theater. If there are no EVs that can perform the military mission as well as ICE vehicles by 2050, which I suspect will be true, then they will just go out and buy ICE vehicles but they will just add more paperwork to make it seem that they aren't breaking their own rules.