The Coast used two HO2S-1s to test and develop helicopter dipping Sonar for ASW operations. In January of 1946 LT. Stewart Graham reported to Commander Anti-Submarine Development Detachment VX-1 for temporary duty.
A LST fitted with a platform served as a helicopter carrier, a destroyer served as the control station, two smaller vessels took underwater sound measurements and several submarines – including a captured German U-boat – served as targets. Actual testing began on 22 March using a U.S. Submarine between Key West and Cuba. Success was immediate. The final test was conducted using the German U-boat, the newer type, capable of a sustained 15 knots underwater. The sonar worked very well. Graham later wrote “that once the helicopter sonar tests were analyzed even the most skeptical decision-makers were convinced that the helicopter mounted sonar was a very anti-submarine warfare program.”