In the early 1980s, the remaining steam-heat capable locomotives gravitated to Scotland, eventually replacing both Class 27s on the West Highland Line and Class 26s on the Far North and Kyle of Lochalsh lines. However, their use became tricky once ETH-fitted Mark 2 and Mark 3 coaches moved north. The sleeper trains were a particular problem. To this end, steam-heat 37/0s were coupled to ETHELs (Electric Train Heating Ex-Locomotive - essentially Class 25s with isolated traction motors that provided Electric Train Heating) which provided the necessary power to run them.