Southern Railway (UK) class 4-SUB

4-SUB designated four-car sets for London inner-suburban lines which were introduced by Bulleid in the forties. Based on the 3-SUB sets which had been built from 1915, the new ones had an additional trailer. Some were built new in all-steel construction and others were rebuilt from existing 3-SUB sets by adding an additional all-steel car. Like their predecessors, both end cars were Driving Motor Brake Thirds (DMBT) with two traction motors in the outside bogie, originally with 275 hp each and later with 250 hp. Production continued under British Railways until 1951. While the rebuilt sets were already withdrawn between the late fifties and the late sixties, the new-built ones became class 405 in the TOPS scheme. The last ones operated until 1983.