HMS Orion was a 74-gun third rate ship of the line of the British Royal Navy, launched at Deptford on 1 June 1787 to the design of the Canada class, by William Bately.

In October 1795 Orion recaptured the merchantman Thames, Atterbury, master, which had been among a number of vessels that a French frigate squadron had captured in late September.

In August, Nelson finally caught up with the French fleet, resulting in the Battle of the Nile, where Captain Saumarez was wounded.

In October 1805, now under Captain Edward Codrington, she took part in the Battle of Trafalgar where, with Ajax, she forced the surrender of the French 74-gun ship Intrépide.

On 25 November, Thunderer detained the Ragusan ship Nemesis, which was sailing from Isle de France to Leghorn, Italy, with a cargo of spice, indigo dye, and other goods.