The crankshafts are then geared together to drive a common output shaft.
Each bank of cylinders could be shut down in flight to drive only one propeller, an idea that was reused much later in the Armstrong Siddeley Double Mamba turboprop.
[2] The idea came from the desire to deliver high power in a reliable form for naval use.
Unfortunately, a conventional twin could not be designed so that it came within the size limits for aircraft carrier use on the cramped vessels of the era, even with wing folding; by combining two engines into a single engine block, each powering an independently-driven propeller installed fore-and-aft as contra-rotating units, you could get the power and engine-out safety of a twin engine aircraft in the envelope of a single engine aircraft.
The added benefits included no dangerous asymmetrical thrust if one unit fails, as happens in a conventional twin that loses an engine, and the drag of both engine nacelles can be eliminated and combined within the cross-section of the fuselage.