It was summer. 1690. Instead of visiting the beach and eating icecream, the denizens of Drogheda were more worried about a bloody battle raging just outside their town. A battle with huge consequences for all of Europe, two kings fought for supremacy on the banks of the River Boyne.
Following King James II fleeing to France in 1688, his nephew and son in law William III took the English throne. William came in person to Ireland in June 1690 with a large and well-equipped army composed of Dutch, Germans, Huguenot French and many other nationalities as well as English and Scottish. He was joined by Schomberg and regiments from Londonderry and Enniskillen leaving him with about 35,000 men. James II's army numbered about 25,000 including 6,000 French under Lauzun, but he had few cannon and many of his infantry were ill-trained and poorly equipped. Against the advice of both Tyrconnell and Lauzun, James decided to block William's advance towards Dublin at the River Boyne near Drogheda.
The battle fought at the Boyne on 1st July (by the old calendar then used in the British Isles, 12th July by the present one) was not a great affair in military terms: about 1,000 Jacobites and 500 Williamites were killed (of whom Schomberg was one).
Most of the Jacobite army, and a large part of the Williamite one, saw little action and most of the Jacobite army retreated entact afterwards. By threatening to outflank the Jacobite left, William pinned down many of James's best troops for most of the day while the main Williamite force crossed the river near Oldbridge and overcame stiff resistance including repeated charges by the Irish cavalry. James retreated ahead of his army to Dublin.
Though not by any means the end of the war, the Battle of the Boyne caused James II to quit Ireland but the war continued for another year with William defeating the Irish at Aughrim and the Treaty of Limerick being signed in 1691.