Built for the Ministry of Defence in 1953, WD198 did not enter service until 1956 at the General Stores Sub-Depot at Steventon, moving to Central Ordnance Depot, Bicester in 1958 and finally to HQ Engineer Resources at Long Marston in 1961. Following a long period in store she was restored to working order and given the name 'Royal Engineer' in 1971. A further overhaul followed in 1987/88 and, when withdrawn from service in 1991, she was the last operational steam locomotive owned by the Army. 'Royal Engineer' was part of a collection of railway items acquired by the Royal Corps of Transport Museum Trust for eventual display at a new museum under development at Chatham. As an interim measure 'Royal Engineer' was placed on loan to the Isle of Wight Steam Railway and, following the fitting of Westinghouse air brake equipment, was put to work on passenger services. In 2001 direct responsibility for the care of the locomotive passed to the National Army Museum who confirmed the loan agreement. WD198 can be seen at Havenstreet alongside sister engine Army No.92 'Waggoner', which arrived on the Isle of Wight Steam Railway in February 2005, also on loan from the National Army Museum.

WD198 is currently out of service pending a 'ten year' boiler inspection and overhaul.