Rolls-Royce Pennine

The Rolls-Royce Pennine was a British 46-litre air-cooled sleeve valve engine with 24 cylinders arranged in an X formation. It was an enlarged version of the 22-litre Exe; a prototype engine was built and tested, but never flew. The project was terminated in 1945, being superseded by the jet engine.

A 100-litre 5,000 hp X32 (twin-X16) version of the Exe/Pennine, originally known as the Exe 100, was to have become the Rolls-Royce Snowdon.

Rolls-Royce air-cooled engines, intended for commercial transport aeroplane use, were named after British mountains, e.g. The Pennines and Snowdon.