Fairey P.24 Monarch / Prince 4
The Fairey P.24 Monarch or Prince 4 was a British experimental 2,000 hp (1,490 kW) class H-24 aircraft engine designed and built by Fairey in the late 1930s.
The P.24 Monarch was an enlarged development of the Prince, designed by chief engine designer Captain A.G. Forsyth. Similar in layout to the Napier Dagger the cylinders were arranged vertically in two separate blocks, driving contra-rotating propellers via separate shafts and gears. Like the smaller Prince engine 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. The engine was test flown in a Fairey Battle, serial K9370, with its first flight taking place on 30 June 1939.
At the request of the US, the engine - on the Battle - was sent to America where it was flown at Wright Field for evaluation. The engine did not go into production.