"AJAX" was built by Robert Stephenson & Hawthorns Ltd. and delivered new to Chatham Dockyard. In 1972 the Admirality disposed of all its remaining steam locomotives at Chatham except "AJAX".
During Admiralty ownership, the loco carried the Yard No of 361
"AJAX" was kept in working order and used until the closure of the dockyard in 1984. After the dockyard closed, "AJAX" was placed in secure storage until the opening of the Historic Dockyard in 1985. In December 1986 the locomotive was withdrawn from service for its first 10 year boiler overhaul in preservation. At the end of its 10 year boiler certificate in December 1996, the locomotive was withdrawn from service and placed in store until 1999, when its second major overhaul began, with the locomotive returning to service in 2001.
The locomotive has been taken out of service from end of October 2011 to be completely stripped down for its third major overhaul, details of which can be found on the Locomotive Engineering pages.