The Battle of Trafalgar was the most significant naval engagement of the Napoleonic Wars and a pivotal naval battle of the 19th century. Taking place in October of 1805, the battle saw the British Royal Navy, led by Horatio Nelson aboard the HMS Victory, destroy a combined French and Spanish fleet.
The night prior to the battle, Nelson toured the Victory. Captain Jean-Luc Picard noted the occurrence to Guinan while touring the USS Enterprise-D prior to engaging the Borg on stardate 43997. She noted that Nelson did not return from the battle. Despite this, the battle was won. (TNG: "The Best of Both Worlds")