Battle of Messines
June 7, 1917 - At 2:50 AM on this day, the British Army detonated 19 ammonal mines it had carefully placed beneath the German trenches near the town of Messen, Belgium. 10,000 Germans died in the attack.
The explosion was the deadliest non-nuclear and man-made detonation in history. Preparations started well over a year befor the attack. Engineers from England, Australia, New Zealand and Canada began secretly tunneling under the German trenches and putting 455 tons of explosives in place.
One of the mines left a crater that was 280 feet in diameter and 40 feet deep. Two of the mines failed to detonate, until almost 40 years later when a lightning strike set one of them off. Miraculously, no humans were injured, but a cow was killed.