The blockade of the Vilaine was a naval military operation that followed the Battle of Quiberon Bay, where the French and British fleets clashed during the Seven Years' War off the coast of Brittany.

After the battle, eleven French ships sought refuge in the Vilaine estuary near Damgan, Billiers, and Pénestin, and later moved further inland to Arzal and Camoël to avoid enemy attacks.

For over two years, there was political intrigue among noble officers loyal to Admiral de Conflans, who advocated for the destruction of the stranded ships, and the Duke of Aiguillon, who preferred a gradual departure.

The blockade, enforced by Admiral Hawke's squadron and Officer Robert Duff's unit in the Gulf of Morbihan, was lifted on April 25, 1762, allowing the last French ships to escape to Brest or Rochefort.

By the evening of the battle, seven ships (Glorieux, Robuste, Inflexible, Dragon, Éveillé, Brillant, and Sphinx) accompanied by two frigates (Vestale and Aigrette) and two corvettes (Calypso and Prince Noir) arrived at the entrance to the Vilaine.

[1][2] Guided by local pilots[N 1] and aided by favorable winds and the rising tide, the captains chose to anchor initially at the port of Tréhiguier, a village in Pénestin where a lighthouse was built in 1881.

[4] The ships then moved further into the estuary to Vieille-Roche,[1] a locality in Arzal, an old ferry crossing now the site of the Arzal-Camoël dam since 1970, after unloading their cannons, cannonballs, and chains to lighten their load.

[1] Land forces were mobilized to assist the squadron, with King Louis XV sending officer Beaussier de Châteauvert to the port of Vieille-Roche.

[1] It took over two and a half years of effort for the two officers appointed by the Duke of Aiguillon,[5] Charles-Henri-Louis d’Arsac de Ternay,[N 2] and Charles Jean d’Hector,[N 3] to free the ships from the Vilaine.

[…] we keep them under lock and key, and it would take a miracle to let them out […][5]To pass, they needed exceptional weather conditions: a pitch-dark night, a receding spring tide, and a strong east wind to propel the ships out to sea.

On the night of January 6-7, 1761, amidst heavy fog and later a violent storm, the Dragon and the Brillant, commanded by Ternay and d'Hector, along with the Vestale, the Aigrette, and the Calypso, successfully made their way to Brest or Rochefort.

The Duke of Aiguillon argued for a discreet exit from the Vilaine estuary instead of dismantling the ships, citing the high cost in light of the economic recommendations received.

The officers he recommended (known only to d’Aiguillon at the time of his proposal to Berryer) were the chevaliers de Ternay from the Inflexible and d’Hector, the deputy mayor of the Navy in Brest.

The plan involved Ternay taking leave to remove him from his current command and Berryer drafting a false order requesting d’Hector's availability.

This led to the establishment of a "port officer's bureau serving the king's ships" on the quays of La Roche-Bernard, which also boosted local commercial activity to provide food for the crews.

[…] On February 7, 1760, an agreement was reached among the various butchers of La Roche-Bernard for supplying fresh meat to the navy troops at Vieille-Roche […][28]The local effects of the blockade have been the subject of conflicting analyses.

Oton du Hautais documented in 1894 that "[...] on February 16, 1761, Jacques Le Barz, master of the coastal trading vessel Sainte-Anne of Port-Louis, [...] received 144 livres for transporting a cable from Nantes to Vieille-Roche [...] for the service of the king's ships anchored in the Vilaine river."