Introduced in 1942, the Grumman TBF Avenger carrier-based torpedo bomber proved itself a versatile aircraft for the Allies during what remained of World War 2 (1939-1945). Such versatility lent the airframe well to undergoing various experiments and modifications to further expand the tactical value of this fine wartime machine. In all, 9,839 Avengers were built and used by the air services of the United States, Britain, Canada and New Zealand for their part in the war. Other operators (including a rebuilding France) appeared in the post-war period.
The Avenger was a naturally large and heavy aircraft for its role in delivering torpedo loads over long ranges. However, to extract every ounce of value from the airframe, designers continued to pour more and more into the frame to help expand its usefulness as the war moved on. This continuous work prompted thinking amongst United States Navy (USN) authorities to find an eventual successor for the Avenger, built along more refined lines and possibly producing a singular replacement effort for the mix of torpedo / dive bombers then in USN service. The primary restriction at the time was large, twin-engined aircraft operating aboard space-strapped carriers, namely the all-important Essex- and Midway-class aircraft carriers where space proved a premium.
Despite this, the Navy eventually approached Grumman to develop a possible contender for the carrierborne bomber role. Grumman designers responded with the "Model G-55" in December of 1942 and a formal proposal followed in March of the following year. Grumman suggested that their aircraft could be made ready for war as soon as May 1945 but of course this was a selling point and wishful thinking to say the least. The Navy nevertheless liked what it heard and approved the venture on August 6th, 1943. The initial commitment would cover two flyable prototypes to prove the design sound.
The resulting aircraft was designated "XTB2F-1" and, using the Avenger as a general starting point, the large attacker would be given a pair of wing-mounted engines (unlike the Avenger's single, nose-mounted powerplant). The crew, avionics, fuel and war load (up to 8,000lb of torpedoes or drop bombs) would be concentrated within the smooth-skinned, rounded fuselage which had a traditional single-finned tail unit at the rear. The nose section was well-glazed to provide for excellent vision out-of-the-cockpit and a radar fit would be carried in a pod under the portside wing. Offset to the starboard side of the nose was a 75mm cannon installation within a blister-style fairing. The portside of the nose stood to receive 2 x 0.50 caliber heavy machine guns and a further 4 x 0.50 caliber machine guns were envisioned in the wings. Unlike the Avenger, the XTB2F-1 was to accomplish ground-running with a tricycle undercarriage to provide for better vision on carrier decks. As was the case with most all carrierborne aircraft, the Grumman G-55 was also given folding wings for storage, the wings hinged just past the main landing gear leg wells and engine nacelles. Additional armament would come from a dorsal turret and ventral turret where each would carry 2 x 0.50 caliber heavy machine guns.
In total, the attacker would be able to rely on a 75mm autocannon, 10 x 12.7mm machine guns and an 8,000lb bomb load (or two torpedoes).
The G-55 grew to become a very impressive aircraft, both large and heavy. Overall weight was estimated to reach in the neighborhood of 45,700lb and the wingspan measured out to 74 feet! To drive this monster was 2 x Pratt & Whitney R-2800-22 air-cooled radial piston engines of 2,100 horsepower, each driving three-bladed propeller units. The aircraft was estimated to end up with a top speed of 335 miles-per-hour and hit an altitude nearing 30,000 feet out to a range of 3,700 miles (ferry).
Grumman completed a mockup of their new bird for USN inspection and this occurred in May of 1944. Within a month, the Navy realized that the XTB2F-1 was not the answer and cancelled the request on June 14th, 1944, ending hopes for the two contracted-for prototypes. The G-55 was simply too large and too heavy for the current-generation carriers in USN service and would deliver far too little for the commitment when compared to smaller attack platforms already in circulation. The USN then moved on to consider other options.