Battle of Trafalgar

Crucial to Napoleon's original plan to invade Britain was his fleet, which had to cover the landing of his army by eliminating or at least distracting the Royal Navy. After Villeneuve had joined his fleet at Toulon with the allied Spanish fleet at Cadiz, he was to sail to the West Indies to attack British possessions there and reinforce French forces in Martinique, for which an additional 12,000 troops were embarked. This was to draw part of the Royal Navy away from European waters. The plan was then to have the combined fleet turn and sail to Brest to rendezvous with the French Atlantic Fleet. With this force, Napoleon then intended to gain naval supremacy in the Channel to secure the planned invasion of Britain.

The British tried to prevent this by blockading the ports of Brest and Toulon. However, on 30 March 1805, the French fleet was able to leave Toulon unnoticed, as the British ships were prevented from effectively blockading by adverse winds. Subsequently, the French ships managed to rendezvous with the Spanish fleet off the Spanish coast and cross the Atlantic. The British Mediterranean fleet under Nelson took up the pursuit but was unable to engage the enemy. Villeneuve, however, did not take advantage of his naval supremacy in the Caribbean, but remained almost inactive. He even refrained from discharging the 12,000 troops. His fleet then consisted of 19 ships of the line and several frigates, while Nelson pursued him across the Atlantic with only nine ships of the line and two frigates.

When the latter arrived in Barbados, Villeneuve, despite his overwhelming superiority, did not seek a decision, but left the Caribbean waters in flight for Europe. The British Admiralty, however, divined Napoleon's plan and ordered Vice-Admiral Robert Calder to sail with his ships to meet the enemy. This fleet succeeded in bringing the numerically superior enemy force to battle off Cape Finisterre on July 22, 1805. The British captured two Spanish ships before the battle was broken off due to poor visibility.

Villeneuve then managed to reinforce his forces with another ten Napoleonic ships of the line, which Calder had previously blockaded at Ferrol. However, disobeying Napoleon's orders, he did not sail on to Brest to engage the Channel Fleet in battle, but sought refuge at Cadiz on 20 August. Allegedly, Villeneuve was given false information about a superior British fleet in the Bay of Biscay, so he disobeyed orders and returned to Cadiz. Thus the French strategic advantage was lost, for now the Royal Navy immediately blockaded Cadiz harbour: initially, however, only with Admiral Cuthbert Collingwood's vastly inferior forces, which were reinforced by Calder's ships on 30 August. Nelson himself initially returned to England, only joining the blockading fleet on 29 September with a further three ships of the line and assuming overall command. Nevertheless, the British were narrowly outnumbered by the enemy.