Napoleon Bonaparte's planned invasion of Britain was known in history as the Third Coalition. In 1805, the year the Third Coalition was formed, Napoleon designed an invasion of Britain. By that time, the royal armed forces of the United Kingdom had emerged as the most powerful armed forces in the world, and Britain, in general, had become the most powerful country.

It was for the purpose of conquering Britain that he began to gather troops and increase the strength of his naval forces. The focus of Napoleon's navy was to force the British naval fleet to withdraw from the English Channel and stop them from advancing and entering France. He hatched a complex plan to distract the British and seize their possessions in the West Indies, but it failed when Admiral's Villeneuve's fleet (a Franco/Spanish fleet) retreated after their actions off Cape Finisterre proved ineffective on July 22, 1805. Admiral Villeneuve was blockaded by the Royal Navy in Cadiz. On October 19, 1805, he left for Naples, and two days later, his fleet was captured and defeated at the Battle of Trafalgar.