The Eastern TBM-3W Avenger was an airborne early warning radar aircraft developed during the Second World War but that only entered service in May 1946. Work on airborne warning radar began early in 1942 at the Radiation Lab at MIT (Project Cadillac). At this point radar was becoming common on warships, but a radar set mounted on a 50ft mast could only detect low flying aircraft at very close range - 20 miles for an aircraft at 500ft. For an aircraft flying at 300mph this only amounted to a four minute warning.
Although the Avenger had not yet entered service it was the obvious aircraft to carry the new radar set, being one of the largest aircraft then operating from carriers, and with a large internal bomb bay. The resulting APS-20 radar set had an 8ft by 3ft antenna, the largest that would fit between the undercarriage legs of the Avenger. The radar set was mounted in the forward part of the bomb bay, with the antenna protected by a massive fibreglass radome. Two radar operators were located in the radio operator's station at the rear of the aircraft, while the turret was removed and a new single place cockpit with a turtle-back fairing replaced the greenhouse. At the same time as gaining a second crewman the radio operator's compartment lost some space as the 'tunnel' was smoothed off to improve the aircraft's rear ground clearance.
The rest of the fuselage was filled with electrical equipment, including two VHF radios, IFF gear, the rest of the radar set and data link relay equipment that could transmit the radar data to another aircraft or to the ground. Finally auxiliary tail fins were added near the tips of the horizontal stabilisers to improve lateral stability.
The XTBM-3W prototype made its maiden flight on 5 August 1944, and was successful enough to encourage the Navy to order a number of conversions. The urgency of this programme dramatically increased after the start of large scale kamikaze attacks, and forty radar sets were produced. Air crews were training with the new aircraft early in 1945, but this training period lasted so long that the war ended before they could join the fleet.
The TBM-3W joined the fleet in May 1946, and was soon paired with the TBM-3S in hunter-killer anti-submarine teams. The powerful radar in the -3W would be used to find a potential Soviet submarine, guiding the -3S onto its target. The -3W remained in service with the US fleet until the mid 1950, when it was replaced by early warning versions of the Grumman AF Guardian and Douglas AD Skyraider.