[2] Similar in layout to the Napier Dagger, the cylinders were arranged vertically in two blocks, driving contra-rotating propellers using separate shafts and gears.

Like the smaller Prince engine, one bank of cylinders could be stopped in flight with the other still driving its own propeller, an idea that was reused much later in the Armstrong Siddeley Double Mamba turboprop.

[3] The engine was test flown in a Fairey Battle, serial K9370, with its first flight taking place on 30 June 1939.

[4] The engine was considered for use in the Hawker Tornado and K9370 was later shipped to Wright Field in the US, where testing (Project MX-229)[5] was carried out in 1942 with a view to using the potentially 3,000 hp of the P.24 in the Republic P-47 Thunderbolt, a total of around 250 hours of test flying in the Battle being completed at Wright Field before the idea was abandoned.

Following cancellation, the engine provided three trouble-free years of service in K9370.