47. Big Whoopsie
Canadian and US forces, allies in the Pacific theater of World War II, planned a coordinated assault to oust Japanese troops from Kiska Island in the Aleutians. Unbeknownst to them, the Japanese had evacuated the island two weeks earlier, leaving it empty of enemy forces.
When the allied troops landed, the dense fog, rugged terrain, and heightened tensions led to a catastrophic mistake: mistaking each other for the enemy, they opened fire. This tragic incident of friendly fire resulted in the deaths of 28 American and 4 Canadian soldiers, with a total of 313 casualties, all without engaging an actual enemy.