First flight on September 21, 1967, the Lockheed CL-840 was the winner of the US Army 's 1965 / 6 AAFSS ( Advanced Aerial Fire Support System ) competition. Grown from the XH-51, was equipped with an additional pusher prop on the tail and had a max. speed of 400 Km/h.

By 1968, 10 pre-production units (serial numbers 66-8826 / 8835) were delivered and others 375 units were approved, but meanwhile the Army acquired AH-1G HueyCobras, a private - venture design of Bell. Finally, by the end of 1969, with Cobras already in Vietnam, the US Army cancelled the AH-56s request.