The Battle of Ulm was a battle of the Napoleonic Wars, fought in 1805 at Ulm in Austria.

In 1805, England, Austria, Sweden and Russia formed the 3rd Coalition to overthrow the French Empire. When Bavaria sided with Napoleon, the Austrians, 72,000 strong under General Baron Mack von Liebereich , prematurely invaded her, while the Russians were still marching through Poland. It brought the Austrians into conflict with the French before the Russians could come into line. Napoleon had 18,000 troops of the Grand Army 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. 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 Gunzburg , but clashed with the French 6th corps, lost 2,000 men and returned to Ulm. By October 16 Napoleon had surrounded his entire army at Ulm and three days later Mack surrendered with 30,000 men. Some 20,000 escaped, 10,000 were killed or wounded and the rest made prisoner. About 6,000 French were killed or wounded. Mack was court-martialled and sentenced to 20 years' imprisonment. On October 21 the French were defeated at Trafalgar.