Battle of Trafalgar
The Battle of Trafalgar was a conflict fought on 21st October 1805 during the Napoleonic Wars between the Royal Navy, led by Lord Admiral Horatio Nelson, and Napoléon Bonaparte's fleet. Although the English won the battle, Admiral Nelson was killed in the fighting.
The Doctor, Ben Jackson and Polly visited Nelson's ship during the battle, during which the Doctor attempted to change history by preventing Nelson from being killed, but was unsuccessful. (DWA: H.M.S. TARDIS) On later occasions, the Doctor made mention of his involvement in the battle. (PDA: Eye of Heaven, EDA: The Scarlet Empress)
The Eleventh Doctor and Amy Pond visited a different ship during the battle, which was fleeing from what they believed to be a Kraken. It was actually a 21st century aircraft carrier brought back in time by an infestation of Time Roaches, which the Doctor sent back into the Time Vortex, causing the carrier to return to its own time. (DWAM: Rough Waters)