Staff Writer (Updated: 5/16/2016):
The TBF Avenger was born from a 1939 US Navy requirement intending to replace the already outclassed Douglas TBD Devastator series of carrierborne torpedo dive bomber aircraft. Despite its rather advanced features when it was introduced in 1937 - these including a fully-enclosed cockpit, retractable undercarriage and stressed metal skin construction - global technology quickly superseded the Douglas design to the point that it was made obsolete at the time of the Japanese attack on Pearl Harbor in December of 1941. Thrust into war, the United States military feverishly attempted to stock its inventory with more adaptable and modern types, ultimately leaving the Devastator out of its plans. The aircraft was withdrawn from frontline duties as soon as 1942 and was officially retired from the USN inventory in 1944, with only 130 having been procured since inception.
Looking to take advantage of the latest in available engines from top manufacturers such as Pratt & Whitney and Wright, the USN fleshed out their latest requirement and the need was responded to by aircraft concerns Vought and Grumman. Vought delivered their XTBU-1 prototype which the US Navy purchased in two evaluation examples. Similarly, two of the XTBF-1 Grumman prototype were ordered and this became the company's first foray into the world of carrier-based torpedo bombers. The Grumman offering consisted of a conventional monoplane design featuring multiple crew and all-metal construction, designed in a mere five weeks under the direction of Grumman engineer Bob Hall. R. Koch contributed the addition of an internal weapons bay to aid in aerodynamics while keeping a ventral machine gun position in place for defense. Oscar Olsen, having worked for General Electric prior, developed an electrically-powered dorsal turret with "Amplidyne" control where the turret's motor could react to the violent changes in loads during flight maneuvers resulting in excellent reaction time for the gunner. The ungainly design earned the aircraft the in-house nicknames of "Turkey" and "Pregnant Beast" for obvious reasons. Primary armament included a fixed, forward-firing 7.62mm gun along the right side of the nose (to be operated by the pilot), a 7.62mm machine gun in a rear-facing ventral position (for the bombardier) and a 12.7mm heavy machine gun in the dorsal powered turret for a dedicated machine gunner.
The US Navy selected the Grumman design as the winner of the competition and placed an order for 286 aircraft on April 8th, 1940 - this before the prototype had even flown. It was not until August 1st, 1941 that the XTBF-1 achieved first flight with chief engineer Bob Hall at the controls and the aircraft powered by a single Wright R-2600-8 14-cylinder Cyclone radial piston engine of 1,700 horsepower. So promising was the design and so dire a need for viable military aircraft for the USN that the initial procurement order was eventually edited to become "open-ended" in nature.