The Great Western Railway branch line from Yelverton to Princetown opened in 1883, amongst other things to serve Dartmoor prison and the local granite industry. Princetown station, said to be the highest railway station in England at 1,373 feet above sea level, was reached after almost continuous gradient from Yelverton which itself was 500 feet about sea level. The sharply-curved line between Yelverton towards Princetown had ruling gradients between 1 in 40 and 1 in 50 for much of its length: the 20 mph speed restriction in this direction was felt to be unnecessary!

This 1931 picture of 4402 at a misty Princetown station shows the unsuccessful Westinghouse equipment fitted next to the smokebox. Picture: Great Western Trust.

Two of the 44XX class 2-6-2 locomotives built in 1905 normally worked the line, usually with the chimney end of the locomotive towards Princetown to keep the firebox crown covered on the gradients. These locomotives had 4ft 1½ inch diameter driving wheels for working branch lines in hilly areas and the class was renowned for rapid acceleration. Number 4402 (pictured) is believed to have spent almost its entire life working the Princetown branch. 4402 was experimentally fitted in 1931 with a Westinghouse compressed air brake to boost braking power. Another refinement added at the same time was a Westinghouse air-operated atomiser system which blew a fine mist of gas oil from oil containe