This Neptune was taken on strength by the US Navy around 1953 as a P2V-5, later modified to P2V-5F and redesigned P-2E in 1962. In the mid-1960s it was loaned to the Army and converted to AP-2E, a designation allocated to draw attention away from the aircraft's role as a SIGINT handling platform (RP-2E would have been more technically correct). From 1967 to 1972 it operated with the 1st Radio Research Company out of Cam Ranh Bay, Vietnam on signals intelligence work. Returned to the Navy in 1973 and retired to the museum by 1981

The US Army operated 12 AP-2E a/c loaned from the US Navy during the Vietnam war. Used from 1965-1972, they were outfitted as signals intelligence aircraft able to intercept low power transmissions. They maintained their former USN paint scheme while being operated by the US Army. 1st Radio Research Company (Aviation) insignia is on the nose under the cockpit windows.