Gone at 3:17

At 3:17 on March 18, 1937, a natural gas leak beneath the London Junior-Senior High School in the oil boomtown made up of London and New London, Texas, created a lethal mixture of gas and oxygen in the school's basement. The odorless, colorless gas went undetected until a flip of an electrical switch triggered a colossel blast that disintegrated one of the nation's most modern schools. More than three hundred students and teachers were killed and hundreds more injured. It remains the deadliest school disaster in U.S. history.