The Battle of Ulm (October 16–19, 1805) was a series of minor skirmishes at the end of Napoleon Bonaparte's Ulm Campaign, culminating in the surrender of an entire Austrian army near Ulm in Württemberg.
In 1805, the United Kingdom, the Austrian Empire, Sweden, and the Russian Empire formed the Third Coalition to overthrow the French Empire. When Bavaria sided with Napoleon, the Austrians, 72,000 strong under General Mack von Leiberich, prematurely invaded while the Russians were still marching through Poland. The Austrians expected the main battles of the war to take place in northern Italy, not Germany, and intended only to protect the Alps from French forces.
A popular but apocryphal legend has it that the Austrians used the Gregorian calendar, the Russians were still using the Julian calendar. This meant that their dates did not correspond, and the Austrians were brought into conflict with the French before the Russians could come into line. This simple but implausible explanation for the Russian army being far behind the Austrian is dismissed by scholar Frederick W. Kagain as "a bizarre myth". In reality, the Austrians expected that northern Italy, rather than Germany, would be the site of major battles.
Napoleon had 177,000 troops of the Grande Armée at Boulogne, ready to invade England. They marched south on August 27 and by September 24 were in position facing General Mack, around Ulm, from Strasbourg to Weißenburg in Bayern. On October 7, Mack learned that Napoleon planned to march round his right flank so as to cut him off from the Russians who were marching via Vienna. He accordingly changed front, placing his left at Ulm and his right at Rain, but the French went on and crossed the Danube at Neuburg.
Trying to extricate himself, Mack attempted to cross the Danube at Günzburg, but clashed with the French VI Corps at Elchingen on October 14 in the Battle of Elchingen. The Austrians lost 2,000 men and returned to Ulm. By October 16, Napoleon had surrounded Mack's entire army at Ulm, and three days later Mack surrendered with 30,000 men, 18 generals, 65 guns, and 40 standards.
Some 20,000 escaped, 10,000 were killed or wounded, and the rest made prisoner. About 6,000 French were killed or wounded. At the surrender, Mack offered his sword and presented himself to Napoleon as "The unfortunate General Mack." Bonaparte smiled and replied, "I give back to the unfortunate General his sword and his freedom, along with my regards to give to his Emperor". Francis II was not as kind, however. Mack was court-martialed and sentenced to two years' imprisonment.
The Ulm Campaign is considered one of the finest examples of a strategic turning movement in military history.