The PRC-77 is the manpack in most people's minds if you ask about military radios. Visually identical to the PRC-25, both served in Viet Nam and into the early 80's when they were made obsolete by frequency hopping. Though there are probably some still in use now. 

Mine is in a mobile mount and I keep it parked on 51.0 Mhz, which is a de facto standard for hams using mil vhf gear as there were standard crystals available. Also the rig does not have the capability to do 5khz steps, so 51.525 is not an option. 

There is quite a bit of good info available on the net, so I won't duplicate it here.