The Rolls-Royce Exe, or Boreas,[1] was a 24-cylinder air-cooled X block sleeve valve aircraft engine intended primarily for the new Fairey Fleet Air Arm aircraft, particularly the Fairey Barracuda.

The Exe was relatively powerful for its era, producing about 1,100 hp (820 kW).

[3] Ernest Hives, head of the Rolls-Royce aero engine division, wanted to stop work on the Exe, Peregrine, and Vulture to concentrate on the Merlin and Griffon engines.

An enlarged version, the Rolls-Royce Pennine, was built later in the war, but cancelled as jet engines became the company's focus.

Originally intended for the Supermarine Type 322 and Fairey Barracuda the Exe was only test flown in a Fairey Battle, the first flight taking place on 30 November 1938.