In 1919 Maunsell decided to rebuild one, N°179, and quite changed the whole look of the engine. The footplate over the driving wheels was raised and the Wainwright cab was replaced with one of the "standard" Maunsell variety. The technical changes involved fitting a new, larger, firebox, replacing slide valves with 10" piston valves and reducing slightly the total heating surface in the boiler and firebox. N°179 hadn't yet been superheated so this was done at the same time, fitting a Maunsell-style header. This, the first E1, was rebuilt at Ashford and proved to be such an improvement on the E class that it was decided to rebuild ten more, which was done during 1920 by Beyer, Peacock & Co.

Following the rebuilding of eleven the E class into the E1 class, 21 of the 51 D class engines were rebuilt as D1 class between 1921 and 1927.  These D1 locomotives were, to all intents and purposes, the same as the E1 class.  Four of the E1s were converted to oil burnring during the 1926 strike, but they didn't remain in this condition for long and were converted back to coal firing.

Originally employed on express passenger trains on the Chatham section, the locos ended their days under BR(S) on secondary lines and stopping passenger duties, although the occasional express service would take them back onto the main line.