Vice-Admiral Sir William Augustus Montagu KCH CB (4 December 1785 – 6 March 1852) was a senior officer of the British Royal Navy during the French Revolutionary and Napoleonic Wars who served in a number of sea battles and was also in command of the naval brigade in the brief land campaign to capture Île de France in 1810. During his service he was present at the capture of numerous French frigates and later served in the War of 1812. After the end of the Napoleonic Wars he remained in service and commanded several ships in the Mediterranean before he retired from active service in 1837. He remained a commissioned officer and later rose through the ranks to become a vice-admiral. For his services he was knighted in the Royal Guelphic Order and made a Companion of the Order of the Bath.
Montagu joined the army young, going to sea aged 11 in 1796 as a volunteer on HMS Glatton commanded by Captain Henry Trollope. Montagu remained with Trollope when he moved, first to HMS Russell in which Montagu saw action at the Battle of Camperdown and subsequently HMS Juste. In late 1800, Montagu was commissioned as a midshipman and joined the frigate HMS Sirius. In Sirius he was present at the capture of Dédaigneuse and then moved into the brig HMS Dasher for four years, spent in the West Indies. In 1804 Montagu returned to Europe as a lieutenant and the following year was promoted to commander.
In 1807, Montagu became a post captain and took command of the small frigate HMS Terpsichore in the Indian Ocean. In March 1808, Terpsichore was attacked by the larger French vessel Sémillante and despite heavy losses, Montagu was able to outfight his opponent although he could not capture her. Soon afterward Montagu moved to HMS Cornwallis and served in the East Indies, forming part of the squadron that captured Amboyna from the Dutch and seized two Dutch frigates in the harbour. By 1810, Montagu was established in the Indian Ocean and was selected from the captains assembled for the Invasion of Île de France to lead the naval brigade, a force of sailors and Royal Marines deployed on shore to support the British Army forces leading the attack. During the assault Montagu fought well and was commended after his brigade assisted in breaking the French resistance around the capital Port Napoleon.