In 1964, when the XV-4A proved unsatisfactory, the remaining Hummingbird was modified with four General Electric J85-GE-19 lift engines (3,000 lb thrust) for hover. Two additional J85 engines provided thrust during horizontal flight. During hover, large diverter valves directed the cruise engine exhaust on each side through the fuselage to a nozzle between the lift engines for additional vertical thrust. In transition, one lift/cruise engine was diverted, while the other provided forward thrust. Pitch and yaw jets at the nose and tail provided control in hover. Maximum vertical take-off weight was 12,600 lb. The Hummingbird II had a fly-by-wire dual channel autostabilization system.

It was rolled out on 4 June 1968 but was destroyed in a crash during a conventional flight on 14 March 1969, without ever making a hover.

Source: AHS V/STOL Wheel