During a crisis meeting headed by the Prime Minister Margaret Thatcher, the Chief of the Naval Staff, Admiral Sir Henry Leach, advised them that "Britain could and should send a task force if the islands are invaded". On 1 April, Leach sent orders to a Royal Navy force carrying out exercises in the Mediterranean to prepare to sail south.
Following the invasion on 2 April, after an emergency meeting of the cabinet, approval was given to form a task force to retake the islands. This was backed in an emergency session of the House of Commons the next day.
The conflict began on 2 April, when Argentina invaded and occupied the Falkland Islands, followed by the invasion of South Georgia the next day, in an attempt to establish the sovereignty it had claimed over them.
On the evening of 3 April, the United Kingdom's United Nations ambassador Sir Anthony Parsons put a draft resolution to the United Nations Security Council.
The nuclear-powered submarine Conqueror set sail from France on 4 April, whilst the two aircraft carriers Invincible and Hermes, in the company of escort vessels, left Portsmouth only a day later.
The Chilean government also allowed the United Kingdom to requisition the refueling vessel RFA Tidepool, which Chile had recently purchased and which had arrived at Arica in Chile on 4 April. The ship left port soon afterwards, bound for Ascention Island through the Panama Canal and stopping at Curacao en route.
On 5 April, the British government dispatched a naval task force to engage the Argentine Navy and Air Force before making an amphibious assault on the islands.
On 6 April, the British Government set up a War Cabinet to provide day-to-day political oversight of the campaign.
The first landings of SAS troops took place on 21 April, but—with the southern hemisphere autumn setting in—the weather was so bad that their landings and others made the next day were all withdrawn after two helicopters crashed in fog on Fortuna Glacier.
On 23 April, a submarine alert was sounded and operations were halted, with Tidespring being withdrawn to deeper water to avoid interception.
On 24 April, the British forces regrouped and headed in to attack.
On 25 April, after resupplying the Argentine garrison in South Georgia, the submarine ARA Santa Fe was spotted on the surface by a Westland Wessex HAS Mk 3 helicopter from HMS Antrim, which attacked the Argentine submarine with depth charges.
The South Georgia force, Operation Paraquet, under the command of Major Guy Sheridan RM, consisted of Marines from 42 Commando, a troop of the Special Air Service (SAS) and Special Boat Service (SBS) troops who were intended to land as reconnaissance forces for an invasion by the Royal Marines.
On 1 May, British operations on the Falklands opened with the "Black Buck 1" attack (of a series of five) on the airfield at Stanley.
On 4 May, two days after the sinking of General Belgrano, the British lost the Type 42 destroyer HMS Sheffield to fire following an Exocet missile strike from the Argentine 2nd Naval Air Fighter/Attack Squadron.
On 14 May the SAS carried out a raid on Pebble Island on the Falklands, where the Argentine Navy had taken over a grass airstrip for FMA IA 58 Pucará light ground-attack aircraft and Beechcraft T-34 Mentors, which resulted in the destruction of several aircraft.
A SAS reconnaissance team was dispatched to carry out preparations for a seaborne infiltration. A Westland Sea King helicopter carrying the assigned team took off from HMS Invincible on the night of 17 May, but bad weather forced it to land 50 miles (80 km) from its target and the mission was aborted.
The tempo of operations increased throughout the first half of May as the United Nations' attempts to mediate a peace were rejected by the Argentinians. The final British negotiating position was presented to Argentina by UN Secretary General Pérez de Cuéllar on 18 May 1982.
On 20 May 1982, Robert Muldoon announced that New Zealand would make HMNZS Canterbury, a Leander-class frigate, available for use where the British thought fit to release a Royal Navy vessel for the Falklands.
The New Zealand government expelled the Argentinian ambassador following the invasion. The Prime Minister, Robert Muldoon, was in London when the war broke out.
During the night of 21 May, the British Amphibious Task Group under the command of Commodore Michael Clapp (Commodore, Amphibious Warfare – COMAW) mounted Operation Sutton, the amphibious landing on beaches around San Carlos Water, on the northwestern coast of East Falkland facing onto Falkland Sound.
From early on 27 May until 28 May, 2 Para, (approximately 500 men) with naval gunfire support from HMS Arrow and artillery support from 8 Commando Battery, Royal Artillery, approached and attacked Darwin and Goose Green, which was held by the Argentine 12th Infantry Regiment.
On 31 May, the M&AWC (The Mountain and Arctic Warfare Cadre) defeated Argentine Special Forces at the skirmish at Top Malo House.
By 1 June, with the arrival of a further 5,000 British troops of the 5th Infantry Brigade, the new British divisional commander, Major General Jeremy Moore RM, had sufficient force to start planning an offensive against Stanley.
Plans were drawn up for half the Welsh Guards to march light on the night of 2 June, whilst the Scots Guards and the second half of the Welsh Guards were to be ferried from San Carlos Water in the Landing Ship Logistics (LSL) Sir Tristram and the landing platform dock (LPD) Intrepid on the night of 5 June.
On the night of 11 June, after several days of painstaking reconnaissance and logistic build-up, British forces launched a brigade-sized night attack against the heavily defended ring of high ground surrounding Stanley. Units of 3 Commando Brigade, supported by naval gunfire from several Royal Navy ships, simultaneously attacked in the Battle of Mount Harriet, Battle of Two Sisters, and Battle of Mount Longdon.
A ceasefire was declared on 14 June and the commander of the Argentine garrison in Stanley, Brigade General Mario Menéndez, surrendered to Major General Jeremy Moore the same day.
The conflict lasted 74 days and ended with the Argentine surrender on 14 June, returning the islands to British control. In total, 649 Argentine military personnel, 255 British military personnel, and three Falkland Islanders died during the hostilities.
On 20 June, the British retook the South Sandwich Islands, which involved accepting the surrender of the Southern Thule Garrison at the Corbeta Uruguay base, and declared hostilities over. Argentina had established Corbeta Uruguay in 1976, but prior to 1982 the United Kingdom had contested the existence of the Argentine base only through diplomatic channels.
The War Cabinet met at least daily until it was dissolved on 12 August.