Abstract: Disclosed is a versatile, compact, explosion resistant, noise reducing, leak-containing structural unit for housing and mounting a variable displacement hydraulic tranmission and its accessories. The structure comprises a protective housing having an access hatch, a hydraulic fluid reservoir integral with the housing, a mounting for receiving a variable displacement hydraulic transmission within the housing, and hydraulic pressure line couplings on the exterior of the housing for connection with a hydraulically driven device. The interior of the housing has mountings for a suction filter, a pressure line filter, relief valves, and a shuttle valve located to facilitate maintenance and promote safety. The transmission may be remotely controlled and is provided with shaft work from a prime mover located outside the housing. The structure, when fitted with suitable components, functions as an interface between any one of a variety of prime movers and a hydraulically driven rotary motion device.