The AN/PRC 77 entered service in 1968 during the Vietnam War as an upgrade to the earlier AN/PRC 25. It differs from its predecessor mainly in that its final power amplifier stage is made up of solid state components and does not use vacuum tubes. The AN/PRC-77 can use voice encryption devices which the AN/PRC-25 cannot. Today the AN/PRC-77 has largely been replaced by SINCGARS radios, but it is still capable of inter-operating with most VHF FM radios used by U.S. and allied ground forces. It is commonly nicknamed the "prick-77" by the U. S. Army and U. S. Marine Corps