On the Pearl Harbor U.S. Naval Base on May 21, 1944, there was a major explosion. Of course this was during World War II so one would think or assume it was another attack, but in fact, this was caused by the U.S. Navy themselves. Before they knew it, a large fire broke out where they kept the Landing Ships, Tanks. This fire then spread onto the Operation Forager that was being prepared for another Japanese attack. The final result of this massive fire was six sunken Landing Ships, Tanks, 163 fatalities and 396 injuries.

So, what exactly happened? The probably cause was determined to be an operation error when unloading a mortar round. It detonated on the spot and the fire spread from there. The U.S. Navy couldn’t let this incident repeat so they immediately began implementing a corrective action to change their weapon handling practices.

(Resource: https://en.wikipedia.org/wiki/West_Loch_disaster)