Thought this that I ran across in Hemmings might be of interest to J.A.W. in particular since he has an affinity for two strokes.
This Vincent engine was commissioned for the R.A.F.
This 1942 vintage lifeboat engine was built by British motorcycle manufacturing legend Vincent during World War II.
Its purpose was to power lightweight Royal Air Force rescue boats that could be dropped from aircraft to dart across the sea to pick up downed pilots.
The 500-cc two-stroke made 15 h-p at 3,000 rpm and would've shoved a small boat along at about 5 knots. Five of these Vincent marine engines were ordered by the British Air Ministry, with an additional order for seven more coming after initial testing. Several of the engine components were interchangeable with an electrical generator engine the company was also producing for the British Army at that time. Vincent delivered all 12 engines, but they were never put into use.
When the RAF initially requested the engines, Phil Vincent already held patents for a two-stroke that would meet the specifications. Vincent HRD designer Phil Irving supervised the final engineering of the engine to bring it into production. The powerplant was based on a three-cylinder block with each outside cylinder providing the horsepower, while the center bore served as a scavenging pump. It contained dual pistons that helped draw in the air fuel mix and suck out the spent gases. The propeller for the outdrive was attached directly to the end of the crankshaft by means of a rag-joint type coupler.