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 Tonnant class. 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.

The Tonnant class was a series of eight 80-gun ships of the line designed in 1787 by Jacques-Noël Sané, whose plans for the prototype were approved on 29 September 1787. With sixteen gunports on the lower deck on each side these were the most effective two-deckers of their era. Their broadside of 1,102 livres equated to 1,190 British pounds weight, over 50% more than the standard British 74-gun ship, and even greater than that of a British 100-gun three-decker.