Книга: Allison T40: Allison Engine Company, Allison T38, Allison T56, Armstrong Siddeley Double Mamba, Pratt, Continental T51, A2D Skyshark, A2J Super Savage, ... engines, R3Y Tradewind, Hiller X-18

The Allison T40 was an early turboprop engine, composed of two Allison T38 power sections driving a common gearbox. The T40 was an attempt to produce a high power turboprop engine by combining two T38 engines side-by-side with a joint gearbox to combine power and reduce shaft speed to that necessary for a propeller. This combination was used with a contra-rotating propellers system. In the late 1940s and early 1950s this engine was favored by the US Navy and was used in several aircraft, the XA2D, XA2J, P5Y, R3Y, and the several VTOL developments including the Hiller X-18, the XFV-1, and XFY-1. The USAF's XF-84H Thunderscreech also tried this engine with a single 3-bladed propeller.