The Battle of Trafalgar was the most significant naval engagement of the Napoleonic Wars and the 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")
An ancestor of Picard's fought in the battle. (Star Trek Generations)