By 1740, war had engulfed Europe. Confrontation in the Caribbean between Spain and Britain led to open hostilities in 1739. Meanwhile, the French had become embroiled in the War of the Austrian Succession (1740-1748). By 1744, France, Spain, Bavaria, and Prussia had formed an alliance to face the combined forces of Britain, Holland, Austria, and Saxony. The struggle between France and Britain spread to North America.
When news of the war reached New France, Governor DuChambon of Louisbourg quickly assembled troops to take Annapolis Royal (Port Royal). Although the attack on Annapolis Royal failed, the French force returned to Louisbourg with captured British ships and their cargos. In response, William Shirley, the Governor of Massachusetts, made preparations for an assault on Louisbourg. He appointed William Pepperell to command the expedition. The British force was composed of militia from Massachusetts, Connecticut, and Maine. Pepperell transported his 4,000 men in 13 American ships escorted by 4 Royal Navy warships. Commodore Peter Warren of Britain commanded the naval forces.
The invasion fleet reached Louisbourg on 30 April 1745. The Anglo-American troops landed unopposed and quickly seized the Royal Battery, a fortified artillery position outside the French fortress. Pepperell's men promptly turned the captured cannon on Louisbourg. The Royal Navy blockaded the harbour and intercepted the Vigilant, a French ship carrying ammunition and reinforcements to the beleaguered fortress.
After subjecting Louisbourg to an incessant bombardment, Pepperell prepared his troops to storm the fortress. Governor DuChambon, however, surrendered Louisbourg before the assault could be carried out. British troops marched into the fortress on 16 June 1745. While the British forces in North America enjoyed some success, the war in Europe did not go in their favour. When peace was finally negotiated with the Treaty of Aix-la-Chapelle on 18 October 1748, Louisbourg was once again a French possession.