The Southern Railway (SR) gave the designation 2-BIL to the DC third rail electric multiple units built during the 1930s to work long-distance semi-fast services on the newly electrified lines from London to Eastbourne, Portsmouth and Reading. This type of unit survived long enough in British Rail ownership to be allocated TOPS Class 401. Construction The 2-BIL units (2-car Bi-Lavatory stock) were so-called because each set had two lavatories, one in each car. They were built in four batches, each for service on newly electrified lines: The different batches were broadly similar, though in the first one, the driving motor brake car had a smaller brake compartment and seven full compartments, rather than six-and-a-half in the later batches. Several of the cars were destroyed in World War II at various points on the system. Some unit numbers were withdrawn, while others received a single replacement car from the small batch of postwar all-steel 2-HAL units which were built as replacements. Formations The first two batches of 2-BIL stock were subject to the EMU renumbering scheme implemented during January and February 1937. The renumbering of these units, and the original formations of all 2-BIL units, are set out in the table below (*Unit 1890 was renumbered 1900 in January 1936): The first ten 2-BIL units (2001 to 2010) had an earlier form of multiple unit control. They were compatible with the 4-LAV units of the same era, but not with the remainder of the 2-BIL sets. They normally operating from Brighton, where the 4-LAV were also based, on local services. The remaining sets spent their lives on the services for which they were constructed, although they were fully mixed in operation, and it was common for units to be exchanged between areas of operation even within a day's normal work. Commuter services into London Waterloo, Victoria and London Bridge found them typically marshalled up to 8-car units. An unusual feature of their operation in the 1950s and 1960s was that there were about 30 more diagrams for these units than sets actually existed, while for the subsequent 2-HAL units (Class 402) there were more than 30 spare units, so a significant number of the daily 2-BIL diagrams were operated by the latter units, typically marshalled together as one of the sets in a full 8-car formation. 7TC In 1963, a 7-coach trailer set was formed by placing five former 4-SUB trailer