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Wearing no safety equipment except their shirtsleeves, workmen use picks and shovels to dig a Tube tunnel that is still used by commuters today.

The photograph of labourers cutting out the Piccadilly line’s Southgate extension in the early Thirties is part of a new mega-tunnels exhibition at the London Transport Museum in Covent Garden and reveals how workers risked injuries such as the bends and even death by drowning from flooding.

The Digging Deeper exhibition explores why these projects have lasted so long, including Brunel’s Thames Tunnel between Rotherhithe and Wapping, completed in 1843 and still used today by the Overground.

A crucial breakthrough in tunnelling technology was an iron circular “shield” giving temporary protection from clay caving in on crews as they cut through the mud.

London Transport Museum Digging Deeper exhibition 5 show all London Transport Museum Digging Deeper exhibition 1/5 Workers digging the City and South London Railway in 1890s London Transport Museum collection 2/5 Wooden carriages being hauled by electric motors under the river from Tower Hill in 1870 London Transport Museum collection 3/5 An artist's impression of the first commuters using the Tower Subway London Transport Museum collection 4/5 Workers digging the City and South London Railway in 1890s London Transport Museum collection 5/5 An artist's impression of the old King William Street station in the City London Transport Museum collection 1/5 Workers digging the City and South London Railway in 1890s London Transport Museum collection 2/5 Wooden carriages being hauled by electric motors under the river from Tower Hill in 1870 London Transport Museum collection 3/5 An artist's impression of the first commuters using the Tower Subway London Transport Museum collection 4/5 Workers digging the City and South London Railway in 1890s London Transport Museum collection 5/5 An artist's impression of the old King William Street station in the City London Transport Museum collection

A giant, automated version of the shield is used today for projects such as Crossrail.

A circular shield was first used to carve out the Tower Subway in 1869, which ran under the river from Tower Hill to Vine Street, near London Bridge.

Sam Mullins, the museum director, said: “A shield which labourers could cut tunnels in and be safe in digging out the London clay was the crucial technical tool for the first tube railways. All the big boring machines today on Crossrail essentially mechanise that process.”

Entry is £17.50 for adults and free for children.