Undermining the positions of the enemy is one of the most ancient activities. For almost 3000 years even before 1914, it was a popular siege-breaking technique. During the Great War arguably the greatest siege the world had ever seen, it presented a conflict environment that perfectly favoured the skills of the military miner. 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. Royal Engineer tunnelling companies were specialist units of the Corps of Royal Engineers within the British Army, formed to dig attacking tunnels under enemy lines during the First World War. The Cornish Miners were one of these specialist units recruited from the tin mines of Cornwall. 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.