oldmachinepress.com
Rolls-Royce Exe (Boreas) and Pennine Aircraft Engines
From the late 1930s to the mid-1940s, Rolls-Royce developed two air-cooled X-24 aircraft engines: the 1,200 hp (895 kW) Exe and the 2,800 hp (2,088 kW) Pennine. Neither engine entered production.