HMS Tonnant () was an 80-gun ship of the line of the Royal Navy. She had previously been Tonnant of the French Navy and the lead ship of the . The British captured her in August 1793 during the Siege of Toulon but the French recaptured her when the siege was broken in December. Rear-Admiral Horatio Nelson captured her at Aboukir Bay off the coast of Egypt at the Battle of the Nile on 1 August 1798. She was taken into British service as HMS Tonnant. She went on to fight at the Battle of Trafalgar in 1805, during the Napoleonic Wars.
Tonnant became the flagship of Vice-Admiral Sir Alexander Cochrane when he assumed command of the North American Station in March of 1814 during the War of 1812 with the United States. On 7 September 1814 Francis Scott Key and John Stuart Skinner dined aboard the ship while seeking the release of a captured civilian prisoner, several days before the Battle of Baltimore. Key went on to write what later became the words to the American national anthem, "The Star-Spangled Banner" after watching the British attack on Baltimore's Fort McHenry. Tonnant was broken up in 1821.
French service
thumb|left|Death of Du Petit-Thouars, by [[Auguste Mayer]]
Tonnant was the lead ship in a class of 80-gun two-deckers built to a design by Jacques-Noël Sané, and ordered on 19 October 1787. She was laid down at the Toulon Dockyard in November 1787 and launched on 24 October 1789. Anglo-Spanish forces captured her there in August 1793, but left her when they withdrew in December. She then reverted to the French Navy.
Tonnant fought in the battles of Genoa on 14 March 1795 and The Nile on 1 August 1798 under Aristide Aubert Du Petit Thouars. During the battle, she severely damaged , causing nearly two hundred casualties, including 50 killed and 143 wounded. Among the dead was Majestics captain, George Blagdon Westcott. Du Petit-Thouars, who had both legs and an arm shot off, commanded his ship until he died. Tonnant was the only French ship still engaged in the morning, with her colours flying, though aground. It was not until 3 August that she finally struck her colours.
The British took her into their service, registering and naming her as HMS Tonnant on 9 December 1798. She arrived at the naval base at Plymouth, England on 17 July 1799. Even before she formally entered British service, she was among the vessels that participated in the capture of the Greek vessel Ardito on 24 October 1798.
Tonnant was commissioned under Captain Loftus Bland in January 1799, with Captain Robert Lewis Fitzgerald taking over in February. He sailed her to Gibraltar and then back to Britain. Upon her arrival in Plymouth in 1800 she was laid up in ordinary.
British service
Napoleonic Wars
Tonnant underwent repairs between December 1801 and April 1803. She was commissioned in March 1803 under Captain Sir Edward Pellew. Under his command she participated in the Blockade of Ferrol.
On 24 May the cutter Resolution captured Esperance and Vigilant, with Tonnant sharing in the capture. Next, Tonnant, and captured the Dutch ships Coffee Baum and Maasluys on 2 and 4 June. Tonnant then was one of the vessels that shared in the recapture on 27 August of .
Tonnant was part of Rear-Admiral Sir Robert Calder's squadron off Cape Ortegal when she encountered the French ships Duguay-Trouin and Guerrière on 2 September 1803. The two French Navy warships had broken out of the blockade when they met Tonnant. They escaped her but British naval forces of varying strengths harried them during their journey back to port and they only just made it to the safety of A Coruña.
Tonnant shared in the capture of Perseverance on 28 October, though the prize money was much less.