During 1915, the Western Front was established as a static line that grew into a huge network of defence-in-depth earthworks. Siege conditions demanded siege tactics and as the ground was everywhere mineable, the Western Front was a prime candidate for underground warfare. In February 1915, eight Tunnelling Companies were created and operational in Flanders from March 1915. By mid-1916, the British Army had around 25,000 trained tunnellers, mostly volunteers taken from mining communities. This is their story.