The Germans, ignoring international treaties they signed, were first to weaponize a chemical. In this case it was chlorine–a highly toxic ingredient used in the manufacture of chemical dyes of which they had a huge supply. Their action unleashed an escalation of poison gas weapons as both sides developed different chemicals and more effective counter measures. Their use of culminated in a bold British plan that unfolded beneath the battlefield at Messine Ridge. British mining and explosive experts planted 450 tons of high explosive hidden in a network of tunnels under Messine ridge. When ignited, they created the biggest land mine in history–killing 10,000 German soldiers. The explosion rattled windows at 10 Downing St., 140 miles away and registered as an earthquake in Switzerland.