Possible Clues:

• Rail track supports
• Dozers on the train or beneath it?
• Beneath the train or part of it?
• Peerless (anag.)
• They may be in, and must be under, the train
• Peerless misreading between the lines?
• They give their support to British lines - and others
• Surprise successes
• Under, and maybe in, train
• They support the rails