There's a bit of both going on, the military did make use of some portable equipment developed by Bell System family companies including WECo. But for the most

There's a bit of both going on, the military did make use of some portable equipment developed by Bell System family companies including WECo. But for the most part, military transportable equipment into the cold war was made by RCA. RCA was more of a "manufacture for sale" type operation than AT&T and had more expertise in portable equipment. Of course, AT&T was one of the founders of RCA, but by the time microwave and troposcatter were coming into use AT&T had sold their shares. Nonetheless there was plenty of technical interchange between AT&T and RCA during that period, and some of the RCA equipment for the military was based on Bell Laboratories and WECo work. The military often made practical decisions of whether it was better to field themselves or contract - and so military connectivity was sometimes contracted to AT&T even in surprising situations like overseas. But field-deployable portable systems have always been impractical to contract out and so the military tends to keep its own assets. Other parts of the government took this other directions. The State Department nearly exclusively contracted to AT&T including for foreign installations. The FAA did so surprisingly infrequently, maintaining its own expansive microwave network until just recently.