During the French Revolutionary Wars, the Royal Navy held the islands for nearly seven years as a strategic forward base.

In July 1795, British sailors and marines from the Western Frigate Squadron under the command of Captain Sir Sidney Smith in HMS Diamond occupied the islands.

Smith dedicated several gunvessels, including Badger, Hawke, Shark, and Sandfly, the last purpose-built for the role, to provide materials and manpower for fortifying the islands and establishing a naval garrison.

In December 1795, the crew of Shark mutinied, in part because of the harsh conditions on the islands, and handed her over to the French.

On 12 September, Robert Fulton sailed his submarine Nautilus to Growan, near Isigny-sur-Mer, a small harbour near the islands.

The main structure is a circular fort with a diameter of 53 meters, with 48 firing ports for cannon on two levels of 24 casemates each.

Later construction, between 1860 and 1867, added a quay, a powder magazine, and a semaphore station, the whole encircled with moats carved into the rock.

In World War II, the islands became the first French territory that seaborne Allied forces took on D-Day.

[3] The French government directly administers the islands, which have the status of a protected nature reserve with restricted access.

Since 2003, the association "Les amis de l'île du large Saint-Marcouf" (Friends of Saint-Marcouf), together with students from the Collège de Carentan, have initiated a campaign to convince the authorities once again to permit recreational access to the Île du Large.