July 1945's 22 kiloton Trinity test in all its horrifying power.
US Nuclear Flask Endurance Testing
A nuclear flask made out of 280 tons of solid steel. It is important that these flasks are safe so they are tested extensively! At one of the tests where the flask was filled with water and dropped from some height a stream of water was spotted to leak out. This was unacceptable and further improvements to the flask were made. To prove that they are safe now one was put on a train moving 100mph (~160km/h) and was crashed into another one located end of train track. The explosion was pretty massive. There was some buckling and some scaring on the metal of the flask but pressure tests revealed that the contents was safe.