Action of 21 July 1781
The Action of 21 July 1781 took place during the American Revolution between two French Navy frigates and a convoy of 18 British ships under protection of the Royal Navy off the harbour of Spanish River, Cape Breton, Nova Scotia (present-day Sydney, Nova Scotia). The two French frigates were led by Admiral Latouche Tréville and La Pérouse, and were ultimately victorious in the battle.
The attack took place in the context of the Franco-American alliance against Great Britain in the American Revolutionary War. There was possible reason that the French attacked; maybe it was because they wanted back Louisburg, that the British took from them in the French and Indian War. 
The British convoy was bound for Spanish River on Cape Breton Island to pick up coal for delivery to Halifax. It was composed of 18 ships, including 9 coal-transporting ships and 4 supply ships. The escorting ships were the frigate Charlestown (28), the two sloops Allegiance (24) and Vulture (20), the armed transport Vernon (14), and another small armed ship Jack (14).
The two French frigates Astrée (38), commanded by La Pérouse, and the Hermione (34), commanded by Latouche Tréville, attacked the convoy. The French severely damaged the Charlestown, which lost her mainmast and a number of her officers, including Captain Francis Evans. The French also significantly damaged Jack, which too lost her captain, and subsequently struck her colors. The engagement ended with the fall of night. Captain George of the British ship Vulture led the damaged escorts into harbor. Six French sailors were killed and 17 British.
While the British escort was severely damaged, the convoy picked up a load of coal at Spanish River and delivered it to Halifax. The French captured the British ship Thorn off Halifax Harbour, along with three merchantmen, which they brought back to Boston. (The following year, the British recaptured Jack in the Naval battle off Halifax.)
The two French commanders would become particularly famous, as Latouche Tréville became an Admiral and a hero of the Napoleonic war, and La Pérouse became a famous explorer. One of the ships, the Hermione, had brought La Fayette to the United States, and a copy is now under construction in the original docks of Rochefort.
Images of the Battle
French frigate Astrée at the battle off Cape Breton
French frigate Hermione at the battle off Cape Breton
Hermione in combat off Cape Breton. Combat Naval A La Hauteur De Louisbourg by Auguste-Louis de Rossel de Cercy.
- (French: Combat naval en vue de Louisbourg, or Combat naval à la hauteur de Louisbourg)
- History of the origin, formation, and adoption of the Constitution of the United States George Ticknor Curtis, p.156 
- Brian Douglas Tennyson and Roger Flynn Sarty (2002), Guardian of the Gulf, University of Toronto Press. Pages 18-19
- Frigates and Foremasts: The North American Squadron in Nova Scotia Waters, 1745- 1815 by Julian Gwyn p.72-3
- Ashore and afloat by Julian Gwyn p.155 
- Gwyn, Julian, Ashore and afloat
- Gwyn, Julian (2004), Frigates and Foremasts: The North American Squadron in Nova Scotia. Waters, 1745–1815, UBC Press.
- Murdoch, Beamish, A History of Nova-Scotia, or Acadie.