Waterloo Day is observed in the United Kingdom every June 18, commemorating the Battle of Waterloo, where the armies of the Seventh Coalition defeated Napoleon's troops in 1815. This battle marked the end of Napoleon's rule after his return from exile on Elba, initiating the period known as the Hundred Days. The allied forces, including troops from the United Kingdom, the Netherlands, Hanover, Nassau, Brunswick, and Prussia, were led by Gebhard von Blücher and the Duke of Wellington, whose contributions were pivotal to the coalition's victory. Celebrations typically involve military parades and reenactments of the battle, particularly among certain regiments of the British Army, highlighting the historical significance of this event in British military history.