HMS Spy was a Bonetta-class sloop launched at Rotherhithe in 1756 for the Royal Navy.

Then from 1780 to 1783, as Mars, she was first a privateer and then a slave ship, engaged in the triangular trade in enslaved persons.

[5] Bayne was also her commander when Spy captured the French privateer Banaba on 29 December 1758.

From this volume on, throughout her history and name changes, the register gave her launch year as 1758, and her origins as the "King's Yard, perhaps because she was completed at the Royal Dockyards at Deptford.

[4] Lloyd's List reported in January 1781 that the privateer Mars had sent into Dartmouth a Dutch vessel that had been sailing from Lisbon to Rouen with a cargo of cotton, rice, etc.

Slave trading voyage (1782–1783): Captain Robert Patterson sailed from London on 14 January 1782, bound for the Gold Coast.

Mars started acquiring captives on 30 April, first at Cape Coast Castle, and then at Anomabu.

1st whaling voyage (1787–1788): Captain William Aikin (or Aiken), sailed from London on 31 August 1787, bound for the Brazil Banks.

[2] 2nd whaling voyage (1788–1789): Captain Akin (or Atkinson) sailed from Southampton on 28 August 1788, for the southern fishery.

[2] In a letter dated 1 December 1788 Akin reported that Southampton was on the Brazil Coast in latitude 35°30'S.

[2] 3rd whaling voyage (1789–1790): Captain A. Muirhead from Southampton on 11 September 1789, bound for Walvis Bay.