WWI underground: Unearthing the hidden tunnel war

Archaeologists are beginning the most detailed ever study of a Western Front battlefield, an untouched site where 28 British tunnellers lie entombed after dying during brutal underground warfare. For WWI historians, it's the "holy grail".

When military historian Jeremy Banning stepped on to a patch of rough scrubland in northern France four months ago, the hairs on the back of his neck stood up.

The privately-owned land in the sleepy rural village of La Boisselle had been practically untouched since fighting ceased in 1918, remaining one of the most poignant sites of the Battle of the Somme.

In his hand was a selection of grainy photographs of some of the British tunnellers killed in bloody subterranean battles there, and who lay permanently entombed directly under his feet.

When most people think of WWI, they think of trench warfare interrupted by occasional offensives, with men charging between the lines. But with the static nature of the war, military mining played a big part in the tactics on both sides....