In 1931, the V-770 design was built, derived from the Ranger 6-440 series of inverted inline air-cooled engines, and test flown in the Vought XSO2U-1 Scout. In 1938 it was tested in the Curtiss SO3C Seamew but was found to be unreliable with a tendency to overheat in low-speed flight, but would still be the most produced aircraft to have the V-770, with 795 being built. By 1941 a more developed V-770 was installed in the Fairchild XAT-14 Gunner prototype gunnery school aircraft, which went into limited production as the Fairchild AT-21 Gunner, of which 174 were built, not including one radial engine prototype. Produced from 1941 to 1945, the V-770 featured a two-piece aluminum alloy crankcase, steel cylinder barrels with integral aluminum alloy fins and aluminum alloy heads. The V-770 was the only American inverted V-12 air-cooled engine to reach production. The engine was used in very few aircraft, among them the short lived Fairchild AT-21 twin-engine bomber trainer, and in the two Bell XP-77 light-weight fighter prototypes.
Variants
;V-770-4: Installed in the Vought XSO2U-1 scout aircraft ;V-770-6: Installed in the Fairchild XAT-14 Gunner prototype, intended for the Ryan SOR-1 Scout ;V-770-7: Installed in the Bell XP-77 lightweight fighter prototype ;V-770-8: Installed in the Curtiss SO3C Seamew Scout. ;V-770-9: Installed in the North American XAT-6E Texan prototype. ;V-770-11: Installed in the Fairchild AT-21 Gunner. ;V-770-15: Installed in the Fairchild AT-21 Gunner. ;V-770-17: Similar to V-770-8 but with raised hollow propeller shaft for mounting cannon or machine gun. ;GV-770: Geared un-supercharged variants. ;SV-770: Supercharged direct-drive variants. ;SGV-770: Supercharged and geared variants. ;SGV-770C-1: Tested in the Curtiss XF6C-7 Hawk fighter-bomber at. ;SGV-770C-1B: ;SGV-770C-2A: ;SGV-770C-B1: Installed in the Ikarus 214 prototype ;SGV-770D-4: Similar to C-2A but with raised hollow propeller shaft for mounting cannon or machine gun. ;SGV-770D-5: Developed for post-war commercial use, at 3,600 RPM, weight, height, length, width
