Earthquaking the Ridge

S1 E2: By 1917 German troops had been facing the British in trenches at Messines for almost three years. Archaeologists discover German tunnels - evidence of an underground war. A camera is lowered down a flooded German mineshaft to looking for remnants of this subterranean battleground because on one night here 19 bombs were detonated beneath German strongpoints killing 10,000 German soldiers in seconds and creating the biggest explosion that the world had ever seen.