<blockquote>Underground warfare was a 24-hour business - shifts worked eight hours on, 16 off. The Givenchy tunnels were very wet, claustrophobic and constricted, typically measuring about 4 ft 6in (130cm) by 2ft 3in (69cm).</blockquote>
via <a href="http://www.bbc.com/news/magazine-36685270">The 18 sewer men who changed the war - BBC News</a>.