sentences:  Taking advantage of this effort, the US Navy awarded Allison a contract for the design and development of a turboprop engine.The resulting T40 combined two Allison T38-A-1 power sections side-by-side with a common reduction gearbox powering contra-rotating propellers.Similar in layout to the Armstrong Siddeley Double Mamba, the T40 differed in that each engine drove both the forward and the rear propellers, unlike the Double Mamba, where each Mamba power section drove either the front or the rear propeller separately.