The Pratt & Whitney R-1535 Twin Wasp Junior was an engine used in American aircraft in the 1930s. The engine was introduced in 1932 as a 14-cylinder version of the 9-cylinder R-985. It was a two-row, air-cooled radial design. Displacement was 1,535 cu in (25.2 l); bore and stroke were both 5+3⁄16 in (132 mm).