The RCH wagon design on 10ft wheelbase chassis was confirmed in 1917 and remained unchanged until after the Second World War. Just before the war, wooden frames were dropped and inspection gantries around the tank top manhole began to appear. Many 10ft 14T tank wagons were built during the war for the Petroleum Board and these passed to the private sector after the war.

The next major change came in 1944 with the move to anchor-fixing of the tank to the chassis and the elimination of the need for end stanchions and fixing stays which had been such familiar features of tank wagon design up to then. The 20T 12ft wheelbase tank wagon also arrived at this time but it was not until 1958 that the 'Monobloc' tank wagons started to appear.