The Grumman AF Guardian is the first purpose-built anti-submarine warfare (ASW) carrier-based aircraft to enter service with the United States Navy. It consisted of two airframe variants, one for detection gear, the other for weapons. The Guardian remained in service until August 1955, when it was replaced by the twin-engined Grumman S-2 Tracker. The Guardian was the largest single-engine piston-powered carrier aircraft ever to see service. Design and development The original design concept for the aircraft that would become the Guardian, the XTB2F of 1944, was for a twin-engined aircraft with a warload and a range of 3,700 mi (5,950 km). This was considered to be too large for practical use from an , and was cancelled in 1945, replaced by a modified Grumman F7F Tigercat, the XTSF-1. However, this too was considered impractical, and another alternative, the internally developed Grumman Model G-70, was selected instead, being given the Navy designation XTB3F-1. This was designed as mixed-power aircraft, with a Pratt & Whitney Double Wasp radial engine in the nose and a Westinghouse 19XB (J30) turbojet in the tail. Originally, the Westinghouse engine was to be the new X24C, which was to emerge as the J34. When it became apparent the X24C delivery schedules would not meet the airframe schedule, the 19XB-2B was substituted. This was found to be unsuitable, and the jet engine was removed without ever having been used in flight. The XTB3F-1S carried a crew of two seated side by side and an armament of two 20 mm cannon and 4,000 lb (1,814 kg) of bombs, torpedoes and/or rockets, and made its first flight on 19 December 1945. On 24 December 1945, the Navy changed the role of the aircraft from torpedo-bomber to anti-submarine warfare. All the required equipment could not be fitted into a single aircraft, consequently two variants would be produced, one as a "guppy" (hunter) and another as a "scrapper" (killer). The hunter aircraft would not carry any armament, but instead two additional crew members and a ventral radome for AN/APS-20 search radar and electronic countermeasures (ECM) consisting of an AN/APR-98 countermeasures receiver and AN/AP-70 bearing indicator. This aircraft, the XTB3F-1S, first flew in November 1948. The "killer" deleted the cannon of the torpedo bomber, but retained the bomb bay, added a third crewmember, a searchlight, and short-range radar, and (as the XTB3F-2S) first flew in January 1949. Operational history Redesignated as AF-2W (TB3F-1S)