A military disaster is when one side in a battle or war is unexpectedly and soundly defeated, and often changes the course of history. A battle where two forces meet and one side loses without making a major mistake is not a military disaster, that is simply warfare.

A military disaster can range from a strong army losing a major battle against a clearly inferior force, to an army being surprised and decimated by a clearly superior force, to a seemingly evenly matched conflict with an extremely one sided result. A military disaster could be due to bad planning, bad execution, bad weather, general lack of skill or ability, the failure of a new piece of military technology, a major blunder, a brilliant move on the part of the enemy, or simply the unexpected presence of an overwhelming enemy force.

Ancient era

• The Athenian expedition to Syracuse in 415 BC.
• The Battle of Cannae in 216 BC, where Hannibal destroyed the sixteen Roman and Allied legions, led by Lucius Aemilius Paullus and Gaius Terentius Varro. In all, perhaps more than 80% of the entire Roman army was dead or captured (including Paullus himself).
• The Battle of Teutoburg Forest, where German warriors destroyed three Roman legions
• The Battle of Adrianople, in which the emperor Valens was killed while Gothic heavy cavalry ambushed and decimated his Roman heavy infantry.
• The Battle of Guan Du, which the more powerful Yuan Shao army failed to guard it's supplies, and was defeated soundly by Cao Cao.

Medieval era

• The Battle of Yarmuk in 636. The Monophysite Ghassanid contingents in the Byzantine army, brutally persecuted by the Orthodox authorities, defected en masse to the Muslim side thus guaranteeing a Muslim victory.
• The Battle of Hattin in 1187, where overconfident Crusader forces from Jerusalem became trapped in a waterless desert area, and thus became easy prey for the Saracen forces of Salah-ud-din (Saladin)
• The Battle of Stirling Bridge in 1297. British Earl John de Warenne's well-equipped army were trapped on a narrow bridge by William Wallace's 15,000 unarmored, lightly-armed Scots, bearing long pointed stakes. The bridge had been chosen as the point of engagement by Warenne, even though the river could easily have been forded just a few miles upstream.
• The Battle of Agincourt in 1415 - A large force of French knights could not operate effectively in muddy conditions, and were therefore mown down by English longbowmen.

16th century

• The Battle of Lepanto in 1571. The Holy League's fleet defeated the Ottoman fleet in the largest naval battle of human history. The Ottomans lost 240 ships (out of about 300), while the he Europeans lost 12 of their 210 ships.

18th century

• Charles XII of Sweden's disastrous wintertime march on Moscow during the Great Northern War marked the beginning of the end of the Swedish Empire.
• The Battle of Karansebes in 1788. A fight broke out between hussars and infantrymen of the Austrian army campaigning against the Ottomans in Wallachia. An officer shouting "Halt! Halt!" was misheard as "Allah! Allah!" causing a mass panic which ultimately resulted in the death or wounding of over 10,000 Austrian soldiers.

19th century

• The Charge of the Light Brigade. A British officer misinterpreted an order and led a suicidal charge against the Russian guns. ("Not tho' the soldier knew, someone had blunder'd" — Tennyson)
• Battle of the Little Bighorn. General George Custer attacks a superior force of armed Native American warriors, gets himself and his entire command killed, the only survivor being a lone horse.
• Battle of Isandlwana. A Zulu impi armed mostly with spears destroys two British battalions armed with rifles in a Pyrrhic victory.
• Napoleon's Invasion of Russia in the winter of 1812 where Napoleon lost almost all of his troops was the turning point of the Napoleonic wars.
• William Elphinstone's disastrous retreat in 1842 during the First Anglo-Afghan War led to the loss of almost his entire command.

20th century

• The Battle of Tsushima - the Russian Baltic fleet was sent halfway around the world in a suicidal attack on the Japanese in the Tsushima Straits in 1905.
• The Maginot line - although from a strictly technical viewpoint the line itself functioned as designed, it was emblematic of a deeply flawed defensive strategy.
• The Battle of France in 1940 - the French Army moved to meet the Germans inside Belgium, believing the Maginot Line would force the Germans to rerun the Schlieffen Plan, but was cutoff by a German advance through the Ardennes, which the French had believed was impassable for tanks.
• The Battle of Taranto in 1940. A small number of British aircraft more or less eliminated the Italian navy by knocking out three battleships with torpedoes as they lay at anchor in the harbor of Taranto.
• The British Operation Compass proved a disaster for the Italian forces in Libya. In the end the British force of 36 000 men captured 130 000 POWs ultimately forcing Germany to dispatch troops of her own to North Africa to save Mussolini from defeat.
• The Japanese surprise attack on Pearl Harbor in 1941 rendered the US Pacific fleet unable to act for six months during which Japan conquered much of the Pacific.
• The sinking of Prince of Wales and Repulse (two battleships) in December 1941 shocked the British and once more showed that aircraft posed a serious threat to even the largest of warships.
• Operation Typhoon, the failed German drive towards Moscow in 1941 was exacerbated by the German decision to not bring along any winter clothing.
• The fall of Singapore (believed to be an impregnable fortress) in February 1942 to two Japanese division was the largest surrender of British-led troops in history and destroyed the lynchpin of the American-British-Dutch-Australian Command.
• The allied Dieppe Raid on German-occupied France in 1942 ended with ~60 % of the attacking force being lost in battle without any of the major objectives of the raid achieved.
• The Battle of Stalingrad in the winter of 1942/43 was one of the turning points of World War II. The German troops in Stalingrad surrendered even though Hitler had promised that they would never leave the city.
• The allied Operation Market Garden in 1944 failed and resulted in the destruction of the British 1st Airborne Division.
• The Battle of Dien Bien Phu, which forced the French to withdraw from northern Vietnam in 1954.
• The Bay of Pigs Invasion, a 1961 attempt to overthrow Cuban President Fidel Castro with 1,500 Cuban exiles. Not only were the exiles heavily outnumbered when they reached the bay, but the US-promised air support never came to aid the exiles.
• The Battle of Longewala, where a 2000 strong Pakistan Infantry Brigade and Armoured Regiment comprising 60+ tanks failed to take a lone Indian outpost manned by a company of just 120 soldiers for hours together and were finally decimated by the Indian Air Force.
• Operation Eagle Claw, a US attempt to rescue hostages in Iran. This operation involved so many opportunities for failure that it was more akin to a Hollywood movie script than an actual military operation.
• Argentinian bombing of Royal Navy ships during the Falklands War. The Argentines flew so low that their bombs hit their targets before the fuzes had time to activate. As a result, the bombs almost always failed to detonate.

Further reading

• Military Intelligence Blunders and Cover-Ups, by Colonel Hughes-Wilson John (ISBN 0786713739)
• Geoffrey Regan's Book Of Military Blunders, by Geoffrey Regan (ISBN 0233999779)

See also

• List of incidents that have been considered great blunders