Dolphin, formerly known as No. 1, was purchased from Doddington House by the Groudle Glen Railway in 1983. Dolphin was built together with Walrus by by the Hunslet Engine Co. Ltd of Leeds in 1952, and supplied to the Tilbury Contracting & Dredging Co Ltd. The engine was resold in 1957, and then transferred to Farnborough (1960) and Doddington House (1969).

Dolphin is a 0-4-0 diesel mechanical, chain driven to each axle, with a Gardner 2LW motor, two speed transmission for each direction of travel, operated by a hand clutch, giving a maximum tractive effort of 2,730 lbs and a top speed of 7 mph.