The V3 engine is a V engine with three cylinders. A V engine with the usual two banks, one bank contains two cylinders, the other only one. A rare configuration, it has only been used for two-stroke racing motorcycles.
The first example was by DKW in the 1960s.
Honda later revived the layout:
A related layout was the W3 or 'fan' engine, although this placed all three cylinders in the same plane, but none of them in the same bank. This was used for the 1905-1915 four-stroke Anzani engine, which was used in motorcycle and aircraft applications.