[1] The 350 cc flat twin engine in the Douglas Mark III was based on a Second World War electricity generator.

[2] During the Second World War the Bristol-based Douglas motorcycle company produced stationary generator engines using their 348 cc overhead valve flat twin.

[1] The result was the 1949 Douglas Mark III, which had improved performance through an uprated cylinder head, combustion chambers, and pistons.

In 1950, he won the Nevis Trophy and the Special First Class Award in the demanding Scottish Six Days Trial riding the Douglas Mark III Competition model.

Securing a win by 19 seconds, Chapman was awarded the Motor Cycling magazine prize for "most meritorious" performance in the Clubmans races.