Her first commander was Captain
Samuel Barrington, who took over in November 1748, and sailed her to the Mediterranean in 1749.
Seahorse was back in the
English Channel in 1752, with
Hugh Palliser replacing Barrington in April 1753.
Seahorse then served initially in Home waters, before sailing to
North America in January 1755. She returned to Britain in July that year, carrying the flag of
Admiral Augustus Keppel. Captain
George Darby took command in 1756, and sailed from Britain bound for
Newfoundland on 15 May 1756. Captain Thomas Taylor replaced Darby in March 1757. Under Taylor's command
Seahorse was active in the
North Sea, later fighting an engagement against two enemy frigates off
Ostend, together with the
sloops HMS Raven and
HMS Bonetta.
Seahorse was then briefly under the command of acting Commander James Hackman from July 1758, before Captain James Smith took over command in October.
Seahorse then left for North America on 14 February 1759, and spent the rest of the year at
Quebec.
Seahorse was surveyed on 24 January 1760 and declared in need of repairs. A large repair was carried out at
Deptford between March and August that year, at a cost of £5,765.19.8d. She fought an action with the French 32-gun frigate
L’Aigrette on 10 January 1761. Captain Charles Cathcart Grant replaced Smith later in the month. She sailed for
India on 4 February 1761 to observe the
transit of Venus, and then moved to
Manila until October 1762 in support of the
Battle of Manila (1762). Captain Robert Jocelyn took command in 1763, after which
Seahorse returned to England and was paid off in June 1763. Further repairs were carried out in 1770, before she was recommissioned in January 1771 under
Thomas Pasley. She sailed to the
Leeward Islands in August that year. In 1773
Digby Dent took command, before
Seahorse was paid off to undergo another refit. She was recommissioned in August 1773 under
George Farmer. Horatio Nelson was assigned to the ship as a
midshipman through the influence of his uncle,
Maurice Suckling. Also a midshipman aboard the
Seahorse at this time was
Thomas Troubridge, another future admiral. Farmer sailed to the
East Indies in November 1773. On 19 February 1775
Seahorse fought a battle with two of
Hyder Ali's
ketches off
Anjengo. John Panton replaced Farmer in June 1777. Early on the morning of 10 August 1778, Admiral
Edward Vernon's squadron, consisting of (Vernon's flagship), ,
Seahorse, , and the
East India Company's ship
Valentine, encountered a French squadron under Admiral François l'Ollivier de Tronjoly that consisted of the 64-gun
ship of the line , the frigate and three smaller ships, , , and . An inconclusive action followed for about two hours in mid-afternoon. The French broke off the action and the British vessels were too damaged to be able to catch them up again. In the action the British suffered 11 men killed and 53 wounded;
Seahorse alone lost three men killed and five wounded.
Seahorse captured
Sartine on 25 August 1778.
Sartine had been patrolling off Pondichery with
Pourvoyeuse when they sighted two
East Indiamen, which were sailing blithely along, unaware of the outbreak of war. The French vessels gave chase lazily.
Sartines captain, Count du Chaillar, first had to be roused from his bed ashore. The British merchant vessels escaped, but
Sartine came too close to Vernon's squadron. He sent
Coventry and
Seahorse after her and she surrendered after a short action. A French account remarks acidly that she surrendered to a frigate of her own size without a fight. All four Royal Navy vessels in Vernon's squadron shared in the prize money. (Vernon had already sent
Valentine off with dispatches.) The Royal Navy took
Sartine into service as the
fifth-rate frigate . By February 1779
Seahorse seems to have been under the command of Alexander M’Coy. Captain Robert Montagu took over command in March 1781, and under him
Seahorse was present at the
battles of Sadras on 17 February 1782,
Providien on 12 April,
Negapatam on 6 July,
Trincomalee on 3 September, and
Cuddalore on 20 June 1783.
Charles Hughes took command in 1783, followed by John Drew in 1784.
Decommissioning and sale Seahorse was paid off for the final time in March 1784. The Navy sold her on 30 December 1784, for the sum of £1,115, to Richard Buller. ==Merchantman==