The Southern Railway (SR) gave the designation SL to the fleet of AC electric multiple units used on the South London lines.

Construction

The SL (South London stock) units were built in 1909 as the first electric train stock for use on the LBSCR AC overhead electrified lines in South London. This stock comprised of eight three-car units, originally formed Driving Motor Third + Trailer First + Driving Motor Third. The Trailer First cars were later removed and used as locomotive-hauled stock, from when the driving cars were paired with former loco-hauled coaches converted to Driving Trailer cars.

After the replacement of the AC overhead equipment by the 750V DC third rail system adopted as standard by the SR, the carriages that formed these units were rebuilt accordingly. The Driving Motor cars were paired together again to form eight units designated 2SL. The Trailer First cars (which had been out of EMU stock for nearly twenty years) were included in this programme, and were rebuilt into Driving Motor and Driving Trailer pairs to form four units designated 2Wim.

Formations

Initial formations of these units were as follows: