Worst military blunders of all time?

[no_rules_just_play]

battle of montgisard: saladin lost 23.000 troops of his 25.000 because he thought the small force of templars (about 300 knights and some thousands of infanterists) wouldnt attack him and was a force that was a danger for his huge army. he left a part of his garrison to block king baldwin (16 years old, leper). he started to attack close-by villages and baldwin charged the troops that saladin left behind (saladin had no idea), he easily crushed them and started to follow saladin. he caught up on monsi gisardi (mont gisard) and crushed the army of saladin that was spread out over a large area and too tired from the long march.
saladin fled back to egypt and when he arrived there 90% of his army was lost due the battle and the bad conditions on the way back. However, he spread word that the muslims had actually won the battle.

[Franke]

Coming to my mind first are various invasions of Russia as someone stated before, too. You may argue about the question, if the Germans under certain circumstances would have been able to succeed in 1941 (earlier start of campaign, securing the support of the ppl of Ukraine, Belarus or the Balts instead of simply slaughtering them), but H.itler's plan to attack Russia with Britain still undefeated in his back is a severe blunder in my eyes. Same with Napoleon's 1812 invasion.
Charles XII of Sweden also invaded Russia and failed. He defeated the Russians at Narva but then turned his attention towards Poland instead of finishing the Russians so they were able to reorganize their army.


There are so many other examples on all kind of scales (Invasion of the Bay of Pigs in 1961, several WWI operations,...).

[Kalam]

I can't believe no one mentioned General Santa Anna's naptime. It's particularly bad because he was generally a competent commander.

[Franke]

I can't believe no one mentioned General Santa Anna's naptime. It's particularly bad because he was generally a competent commander.

Could you go into detail a bit? I know about the Alamo (mostly from that awesome John Wayne movie  ), but generally I don't know too much about the Texans's rebellion.

[Kalam]

Could you go into detail a bit? I know about the Alamo (mostly from that awesome John Wayne movie  ), but generally I don't know too much about the Texans's rebellion.

Admittedly, it's not the worst blunder in the sense of outcomes- there have been far more lopsided battles. The Battle of San Jacinto is the worse in the sense that it could've been completely avoided with one simple practice that's common in every military today, and that it was the crucial battle that allowed Texas to win the war.

So the Mexican Army had the Texan Army and for all intents and purposes, it looked like they were about to win the war. General Santa Anna was leading a professional, trained army that was equipped appropriately. Sam Houston had a militia of random volunteers, bolstered by some folk heroes and a few American veterans.

Right before he thought he was about to win the war, Santa Anna had his Army of roughly 1400 men take a nap. I'm going to type that again. Santa Anna had his men take a nap in the afternoon. A motherfucking siesta. This wouldn't be a big deal, since all men need rest to perform well, it's that he did it without placing any sentries or setting a watch system. It just so happened that Sam Houston decided to launch an attack on them that afternoon. The Texan army (roughly 900 men) caught the Mexicans sleeping, and proceeded to a slaughter. They killed just over 600 of Santa Anna's army, and lost 9 men.

That's when the Texan revolution turned around, and they won the war by capturing the sneaky (he tried to disguise himself) Santa Anna later that day.