HMS Grampus was a 50-gun fourth-rate ship of the line of the Diomede Class of the Royal Navy. She was commissioned in March 1803 at Portsmouth by Captain Hugh Downman, but in the following month command passed to Captain Thomas Gordon Caulfield. The ship was completed on 11 April 1803 and was ordered to the Downs on 7 May. As soon as her complement of men was completed and her bounty paid she sailed to join Admiral Thornborough's squadron off Gorée. She returned to Portsmouth from Guernsey on 20 June to fit out for the East Indies and sailed with a convoy under her protection on 29 June. She carried £100,000 being shipped by the British East India Company to Bengal. She spent 1805 in the East Indies.