London deep-level shelters

The London deep-level shelters are eight deep-level air-raid shelters that were built under London Underground stations during World War II.

Each shelter consists of a pair of parallel tunnels 16 feet 6 inches (5.03 m) in diameter and 1,200 feet (370 m) long. Each tunnel is subdivided into two decks, and each shelter was designed to hold up to 8,000 people. It was planned that after the war the shelters would be used as part of new express tube lines paralleling parts of the existing Northern and Central lines. Existing tube lines typically had 11-foot-8.25-inch (3.56 m) diameter running tunnels and about 21 feet (6.4 m) at stations; thus the shelter tunnels would not have been suitable as platform tunnels and were constructed at stations the new lines would have bypassed. However, they would have been suitable as running tunnels for main-line size trains. (One existing tube, the Northern City Line opened in 1904, used a similar size of tunnel for this reason, although in fact main-line trains did not use it until 1976.)

Ten shelters were originally planned, holding 100,000 people — 10,000 in each shelter. However the final capacity was around 8,000 people in each shelter, and only eight were completed: at Chancery Lane station on the Central line and Belsize Park, Camden Town, Goodge Street, , Clapham North, Clapham Common, and Clapham South on the Northern line. The other two were to be at St. Paul's station on the Central line which was not built due to concern about the stability of the buildings above, and Oval station on the Northern line due to difficult ground conditions encountered as the work started. The working shaft for the shelter at Oval now functions as a ventilation shaft for the station.

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