In late 1944 Grumman started work on what would end up being the biggest single-engined aircraft flown by the US Navy, The "Guardian"as it would be known was a replacement for the "Avenger" torpedo bomber with the company designation of G-70. The aircraft was to be composite powered with 1x Pratt and Whitney piston engine and 1x Westinghouse turbojet engine in the fuselage exhausting at the tail, to give additional power at takeoff and in combat. In February 1945 the US Navy awarded a contract to Grumman for three G-70 prototypes, with the navy designation of XTB3F-1.
Before the flight of the first prototype XTB3F-1(90504) on 19/12/1946, there had being a number of problems with delays of the Westinghouse jet engine, as well as Grumman's work on the F9F "Panther" which caused the XTB3F program to fall behind , this combined with major problems in ground testing with the air intake ducts for the jet engine (they had a tendency to crack and collapse when the jet engine was used!) meant that the first prototype was never flown with the jet engine in operation, and all further aircraft were redesign with out the jet engine.