The Douglas TBD Devastator, the U.S. Navy's main torpedo bomber introduced in 1935, was obsolete by 1939. Bids were accepted from several companies, but Grumman's TBF design was selected as the replacement for the TBD and in April 1940 two prototypes were ordered by the Navy. Designed by Leroy Grumman, the first prototype was called the XTBF-1. It was first flown on 7 August 1941. Although one of the first two prototypes crashed near Brentwood, New York, rapid production continued. The Avenger was the heaviest single-engined aircraft of World War II, and only the USAAF's P-47 Thunderbolt came close to equalling it in maximum loaded weight among all single-engined fighters, being only some 400 pounds (180 kg) lighter than the TBF, by the end of World War II. To ease carrier storage concerns, simultaneously with the F4F-4 model of its Wildcat carrier fighter, Grumman designed the Avenger to also use the new Sto-Wing patented "compound angle" wing-folding mechanism, intended to maximize storage space on an aircraft carrier; the Wildcat's replacement the F6F Hellcat also employed this mechanism. The engine used was the twin-row Wright R-2600-20 Twin Cyclone fourteen-cylinder radial engine, which produced 1,900 horsepower (1,420 kW). Primary users: United States Navy, Royal Navy, Royal Canadian Navy, Royal New Zealand Air Force. Total Number Built: 9,839. For more information on design and development, operational history and variants, click here.