On 2 April Argentina invaded the Falklands.  Known as Operation Rosario (Rosary), it was largely a Navy operation with a major part of that force committed either to the landing force or to its support.  Defending the Falklands were two small detachments of Royal Marines.

Initial landings were by commandos and naval divers followed up by Marine Infantry units, some in amphibious armoured personnel carriers.  In all about 1000 troops were landed initially considerably outnumbering the defenders.  Although a spirited defence was put up it was clear to the 85 Royal Marines and the Governor that a defence could not be sustained.  So later that day the British surrendered, eventually to be repatriated.

The Argentines used the period between invasion and the likely earliest date of British return to reinforce the Islands both in supplies and in building up troop levels to approximately 11,000 as well as constructing defences.  The airfield at Stanley was also secured and warning radars set up.  A significant garrison was established at Goose Green on the west side of East Falkland and an improvised air base was created on Pebble Island.