The reverser (1) is of the type wherein the reversing devices are contained in the leg itself, and comprises two clutches (18, 19) which draw their motion directly from the drive shaft (7). The clutches (18, 19) each act alternately on a driven gear (30) which actuates the propeller shaft (29). Each of the clutches (18, 19) has a hydraulic engagement piston (12, 13). The two hydraulic pistons (12, 13) are fed by a pump (32) keyed on the drive shaft (7) and contained in the body (2) of the aft foot. A hydraulic circuit connects the pump (32) to the pistons (12, 13) through a distributor. The hydraulic circuit is also employed for lubricating all the moving parts of the power leg.