It seems that trying to find some concrete information around Southern EMUs is very difficult. Not only is the information scant and spread between multiple volumes of out-of-print books, but the actual prototype information is dense with numbers, names, formations and units constantly changing. This page is my attempt to straighten out that information. Before you ask, the torpedo-nosed LSWR units will not feature on the layout -
3 Car Suburban Electrics
It's important to note that the '3Sub' definition was never applied to these units at the time, only retrospectively used to identify them in comparison to the later 4Sub units (which were so named)
ex-SECR 3-car suburban set built 1927/28 leading a typical '3Sub + 2 car trailer + 3Sub' formation
These units were built on various underframes using various pre-group coaching stock bodies. There are certain 'tells' as to which pre-group company they originated from - rounded cabs denote some of the original LSWR stock, wide bodies with segmented roof corners indicate ex-LBSCR AC electric stock, etc. Some services could be served by a single 3sub or pair running in tandem, but for any larger capacity an unpowered two-car trailer unit was inserted between. Having no driving cabs however meant that they were not flexible and involved significant 'blind shunting' and the decision was made in 1937 to break up these trailer sets and use those cars to augment the existing units into...
By 1949 all of the original 3-car suburban sets were either augmented into or replaced by 4Sub units. There are two main types, each with two variants.
Type 1 - Pre Group Trailers
Approximately 80 of the 3Sub units were augmented with spare trailers from war-damaged units, or units that were otherwise withdrawn due to non-standard dimensions
(Glen Woods' collection of Ex Brighton unit Nº 4506)
Type 2 - Bulleid Trailers
160ish units outnumbering the 'pure' pre-group 4Subs 2:1 were the slightly odd looking sets that had all-steel Bulleid trailers inserted into them, clearly seen in the second coach below!
4Sub New Builds
Phase 1 "Shebas"
99 units built in 1941-46 of all-steel Bulleid-style bodywork with flat cab sides and multi-segment domed roof - in the range 4101-4110
Phase 2 "Flat Fronts"
77 new units built 1946-48, and full-body rebuilds of the oldest pre-group stock during 48-51
All of the 4sub units were mutually compatible with each other regardless of type or provenance. By the 1950's the limitations of the Westinghouse brake, standard coupling and the low-voltage equipment drove a need to revitalise the fleet which kicked off the production of the 4EPBs. By the end of 1956 almost all of the augmented pre-war 4 Sub units with SR standard underframes had been withdrawn for rebuilding, either as 'new' 4 Sub or as 4 EPB units.
To be continued....