Ulm, Battle of

Series of actions September 1805 during the Napoleonic Wars, generally known as the Campaign of Ulm, in which the French defeated the Austrians in the area of Ulm on the Danube, in southwest Germany. The Austrian commander, General Karl Mack (1752–1828), allowed himself to be surrounded by Napoleon's forces and had to surrender. This paved the way for the occupation of Vienna and a crushing French victory at Austerlitz 2 December 1805.

The Austrians joined the alliance of Britain and Russia against France August 1805, and Mack invaded Bavaria (an ally of France) with 72,000 troops without waiting for Russian troops to join them. Napoleon saw his chance to cut off the Austrians while the Russians were still marching through Poland; he had an army of 180,000 troops at Boulogne, waiting to invade England, and he marched this force south through Hannover and the smaller German states to come up behind the Austrian position and take them by surprise.

Mack reversed his troops but the French moved around his flank; an attempted breakout across the Danube met the French 6th Corps head-on and was rapidly driven back into Ulm. By 16 October Napoleon had completely surrounded the Austrians and three days later Mack surrendered with about 30,000 troops. Of the remainder, 20,000 managed to escape, 10,000 had become casualties in the various skirmishes and actions during the envelopment, and the rest were taken prisoner.