In 1968, the U.S. Air Force canceled a program to convert old Navy submarine hunters into attack aircraft. The flying branch had spent two years trying to get the planes ready for Vietnam.

The project was part of a larger effort to find aircraft that could chase guerrillas around Southeast Asia. The Air Force’s fighter jets and long-range bombers—the bulk of its combat aircraft—were best in a nuclear showdown with the Soviet Union.

These high-performance aircraft, often zipping around at great speeds high above the battlefield, had a tough time finding small insurgent bands on the ground. At night, the situation was even worse.

As the war in Vietnam escalated, so too did the Air Force’s effort to find better warplanes for the conflict. One proposal was to turn old Navy S-2 Tracker anti-submarine planes into ground-attackers.

At the time, the two services were already working on another aircraft exchange. In 1963, the Air Force started getting propeller-driven A-1 Skyraider fighter-bombers from the Navy—and quickly sent them to South Vietnam.

The Navy’s twin-engine Grumman S-2 appeared to be a perfect for the Air Force. The plane already could carry weapons—and Grumman had rigged certain variants for complex electronics.