Admiral Sir Henry Leach: First Sea Lord who convinced Thatcher that Britain must recapture the Falklands

The great test of a military establishment is whether it is able to rise to an unexpected challenge. For this test to succeed it needs firm and forthright leadership.

Admiral Henry Leach showed such leadership as First Sea Lord after hearing the news of the imminent invasion of the Falkland Islands by Argentina in 1982.

With the Chief of the Defence Staff, Lord Lewin, on his way back from New Zealand, on 31 March Leach ignored Lewin's deputy and went straight to the Defence Secretary John Nott in the House of Commons, only to be told that he was in a meeting with the Prime Minister, Margaret Thatcher, and her advisers. Thatcher was uncertain what to do about the invasion, but Leach had no doubt. He told her that the Falklands had to be recaptured. A counter-invasion had to take place immediately: "Because if we do not, or if we pussy-foot in our actions and do not achieve total success, in another few months we shall be living in another country whose word counts for little." A Task Force was assembled and equipped and set sail five days later. The Falkland Islands were retaken in mid-June.

Leach was born in Devon, the son of a naval officer, and was educated at Peter's Court School in Broadstairs, Kent. He joined the naval college at Dartmouth at the age of 14 in 1937. Four years later he was due to join the Prince of Wales but this appointment was cancelled when his father was given command of the ship, so he went to the cruiser Mauritius instead as a plotting officer. In December of 1941, while waiting in Singapore for his ship to be refitted, he met up with his father for a gin sling and a relaxing swim. Two days later, his father's ship, along with the Repulse, was sunk by Japanese aircraft. The young, bereft Leach was seen searching for his father among the survivors who made it back to Singapore, but as captain he had gone down with the ship. The next day a lone Japanese pilot dropped a wreath of flowers to honour the dead of both ships.

As a young lieutenant aged 20 on the Duke of York Leach found himself in charge of "A" Turret with four 14-inch guns with a range of 18 miles. On Boxing Day 1943 the Duke of York went into action in the Battle of the North Cape against the German battleship Scharnhorst, which was on an operation to attack Allied convoys to Russia. At 16.48 starshells were fired to illuminate the enemy. Now with clear visibility, the Duke of York opened fire at a range of 12,000 yards and twice struck the Scharnhorst. But Leach was frustrated when one of his guns became defective. Scharnhorst returned fire, putting two shells through the Duke of York's masts. Scharnhorst's fate was sealed when the Duke of York, firing at extreme range, pierced her armour belt and destroyed a vital boiler, thus reducing her speed. The Duke of York and a number of other ships finally sank this great battleship with a loss of 1,932 men.

Many years later Leach spoke to me of his feelings at the moment of triumph. It was, he said, "almost a blankness of shock at what we had done. Some relief. Little exultation – the closing scenes were too grim for that and that remoteness of action at sea precludes hate between sailors."

After the war, Leach worked in destroyers before specialised gunnery training in 1947 brought him the appointment of gunnery officer of the Newcastle in 1953, with whom he saw action in the latter stages of the Korean War. He gained his first command on the destroyer Dunkirk in 1959.

Leach always had an interest in flying, and while in command of the commando carrier Albion in 1970 he learned to fly helicopters and later flew jets, breaking the sound barrier in a Lightning. He was appointed First Sea Lord in 1979 at the age of 56, where he wisely, in the light of the Falklands War that was to follow, dissuaded the Defence Secretary, John Nott, from scrapping Britain's amphibious ships. In retirement he lived in Winchester, and in 1993 he published a robust but humorous memoir, Endure no Makeshifts.

Henry Conyers Leach, sailor: born Bovey Tracey, Devon 18 November 1923; Chief of Naval Staff and First Sea Lord 1979–82; KCB 1977, GCB 1978; married 1958 Mary Jean McCall (died 1991; two daughters); died 26 April 2011.