Two U.S. Air Force F-15s shoot down two U.S. Army helicopters on a diplomatic mission over Iraq, mistaking them for hostile aircraft in the "no-fly zone, " killing 26 people. No one was found criminally responsible.
A "siesta" ordered by Mexican General Antonio Lopez de Santa Anna to his troops during a conflict between the Mexicans and Texans caused the infantry to be overtaken in just 18 minutes. Fort Douaumont at Verdun in France was captured in 1916 by a single German soldier after French General Chretien forgot to pass on orders to defend the fort to the last man to his successor.
The Russians tried to wreak havoc on German Panzer divisions during the WWII by strapping bombs to the backs of dogs and teaching them to associate food with the underneath of their enemies' tanks. Unfortunately, the dogs only associated food with their own tanks and forced an entire Soviet division to retreat.
Japanese soldier Hiroo Onodo refused to stop fighting long after WWII was over, claiming that stories of the war's ending were mere propaganda. It wasn't until his commanding officer flew out to the remote Pacific island where Onoda was holed up and ordered him to lay down his arms that he finally complied.
Probably the most famous mistake in U.S. military history occurred in the Civil War, when Confederate Gen. Stonewall Jackson was mistakenly shot by one of his own troops after the Confederate triumph at Chancellorsville.