During Vietnam the US Army was looking for a convoy escort aircraft. They did not like the USAF solution of scrambling jet fighters when a convoy of trucks got into trouble. They wanted something overhead all the time.
Grumman proposed a COIN version of the Agcat crop duster. Based on the design of the F3F fighter, the airplane was simple, reliable, very rugged and resistant to ground fire, able to loiter for extended periods, and capable of accurately delivering considerable effective ordnance; the Army concluded it was just what they needed. "How many do you want to buy?" asked Grumman. The Army response was, "What? Us buy a biplane today? It may be exactly what we need but we'd be laughed out of the Pentagon!"