 Throughout the French Revolutionary Wars , British warships patrolled the French coast , intercepting and destroying French maritime traffic and blockading French ports . In 1795 Captain Sir Sidney Smith , a prominent Royal Navy officer , recognised that if resupply points could be established on islands off the French coast then cruising warships could extend their time at sea . To this purpose , Smith seized the uninhabited Îles Saint @-@ Marcouf , which lie 3 @.@ 5 nautical miles ( 6 @.@ 5 km ) off <unk> on the Cotentin peninsula in Normandy . Smith constructed barracks and gun batteries and manned the islands with 500 sailors and Royal Marines , including a large proportion of men unfit for ship @-@ board service , described as " invalids " . The Glengarry Fencibles offered to provide a garrison , but after the French captured Smith this fell through . 
