Throughout his career, Lewin never allowed promotion to change him. A humane and humble man, he always had time for people, no matter what their status.
When the Falklands crisis escalated, Lewin was in New Zealand - 10,000 miles away from his desk in Whitehall. His Flag Lieutenant woke him at 2am on 4 April 1982 with the words: "They've invaded." He did not need to ask who had invaded, or where, and was back in London 28 hours later.
He went from Heathrow to a meeting of the newly formed War Cabinet - Thatcher, William Whitelaw, Francis Pym, John Nott and Cecil Parkinson. The message Lewin delivered to them was grimly resolute: "We must be prepared to take losses. But we are not going to lose. The only thing which will make us lose is if you lose your nerve."
The first ships of the Task Force sailed only five days after the Argentine invasion. It was to carry out an amphibious landing over 8,000 miles away, vastly outnumbered by defending forces and under fierce air attack from shore-based aircraft. British forces were neither prepared nor equipped for the task, having been geared to face a Russian threat close to home. "The truth is the country had no right to expect that we could succeed in this," Lewin was to say later. But they did.
Terence Thornton Lewin was born in 1920 and educated at the Judd School, Tonbridge. He entered the Royal Navy in 1939 and was a cadet on board Belfast at the outbreak of hostilities. The cruiser - now a floating museum on the Thames - was soon crippled by one of the first magnetic mines and Lewin joined the battleship Valiant. After the Norwegian campaign Valiant was involved in the action against the French fleet off the coast of North Africa when the Royal Navy opened fire on the warships of her late ally to prevent their falling into Axis hands.
During three years in the Tribal-class destroyer Ashanti, Lewin won the DSC and was three times mentioned in despatches. Ashanti was involved in the convoys to North Russia, then Operation Pedestal which saved Malta from surrender, and action in the Arctic and in the English Channel during the liberation of Europe.
His DSC was for "high personal example, leadership and outstanding endurance and fortitude" when Ashanti's sister-ship Somali was torpedoed by a U- boat on 20 September 1942 during the passage of Convoy QP14 from Archangel to Loch Ewe. Somali broke in two in a Force 10 gale and began to sink. Lieutenant Lewin went down on a scrambling net to reach survivors in the water, putting himself in great danger of being washed away. He saved the lives of many men that night but the memory of one who was lost was to haunt him. He remembered later: "I grabbed their first lieutenant but the ship was rolling, he was very heavy and covered in oil and I lost him."
After the war, Lewin specialised as a gunnery officer and served in the destroyer Chequers and as a Planning Officer in the Ministry of Defence before returning to sea as captain of Corunna and then commander of the Royal Yacht Britannia. He also found time to represent the Navy at rugby - scoring a try from the wing against the RAF in 1948 - and athletics.
As a Commanding Officer, Lewin used Shakespearean references when sending orders to other ships. An order for a vessel to detach herself from a flotilla would be signalled as a "Macbeth Act 2, Scene 4"; a hurried thumb through the Collected Works would reveal the command: "Avaunt! and quit my sight." Lewin, it was said, would also telegraph his wife with biblical chapter and verse numbers, leaving her to use the Authorised Version to decode his message.
In 1961 Lewin became Captain F of the Dartmouth Training Squadron in the frigates Urchin and Tenby; former cadets recall his close personal interest in each of them and his invitations to tremendously enjoyable group breakfasts in the captain's sea cabin.
After eight years in seagoing appointments, Lewin returned to the Ministry of Defence in 1964 as Director, Naval Tactical and Weapons Policy Division. Here he worked to limit the damage inflicted by the 1966 Defence Review.
He then commanded the aircraft carrier Hermes before returning to the Ministry of Defence in 1968 as a Rear-Admiral and Assistant Chief of Naval Staff (Policy). His final seagoing appointment was as Flag Officer, Second- in-Command, Far East Fleet just before the handover of Britain's Singapore base to the island republic's government.
In 1971 Lewin was promoted Vice-Admiral and became Vice-Chief of the Naval Staff. The inexorable rise continued with promotion to full Admiral in 1973 and appointments as Commander-in-Chief Fleet and Commander-in- Chief Naval Home Command before becoming First Sea Lord in 1977.
It was not an easy time to lead the Royal Navy. Pay levels were well below civilian rates and falling morale had led to record numbers applying to leave the Service. Lewin told sailors that he considered himself "your shop steward" and won them a 32 per cent pay rise.
As Chief of the Defence Staff during the Falklands War, Lewin became, according to one MoD deputy secretary, "the most powerful man in England". A recent reform had elevated CDS to being a genuine, single defence chief rather than chairman of the Chiefs of Staff. This gave him direct access to Margaret Thatcher as her sole military adviser and he quickly won her confidence. Lewin realised that time was crucial in order to achieve victory. He became the key man in the War Cabinet, urging decisive action and leading the politicians rather than passively carrying out their wishes.
On 2 May 1982 Lewin called aside the War Cabinet at Chequers and requested a change in the rules of engagement such that the cruiser General Belgrano could be attacked outside the designated Total Exclusion Zone. Thatcher authorised the change - reputedly in the entrance porch at Chequers. The submarine Conqueror sunk the Belgrano, killing 368 of her sailors. It was the turning-point of the war and of the Thatcher administration. Throughout the ensuing controversy, Lewin remained adamant that he had made the right decision, saying later, "I regret the heavy loss of life and the world- wide concern it caused but I have no regrets at all about sinking the Belgrano."
Even when under intense pressure, Lewin never failed to treat all those with whom he came into contact with the utmost consideration. Early in the Falklands War, two helicopters which had just landed troops on South Georgia were lost during a blizzard. A young radio operator from the destroyer Antrim wrote a letter home which included details of the lost aircraft. The sailor's proud mother showed the letter to a local newspaper, thereby inadvertently releasing information which the Government had deemed secret.
The MoD was furious and there was talk of the sailor's being court-martiallied. The sailor's father wrote to John Nott, the Defence Secretary, apologising for the actions of his son and his wife and requesting that his son be treated leniently. On seeing a copy of the Secretary of State's anodyne reply, Lewin took a pounds 10 note out of his pocket and asked his Flag Lieutenant to send the mother some flowers; he wrote an accompanying note which read: "Please do not worry. You acted as any mother would and I fully understand. With best wishes, Terry Lewin."
When he retired as CDS, Lewin was waved off by an unprecedently large group of staff officers, a number of them moved to tears. He remained very active in public life - as a cross-bencher in the Lords and, notably, as Chairman of the Trustees of the National Maritime Museum - as well as enjoying a particularly happy family life.
Terence Thornton Lewin, naval officer: born Dover 19 November 1920; DSC 1942; Commander, HMY Britannia 1957-58; LVO 1958; Captain F, Dartmouth Training Squadron 1961-63; Director, Naval Tactical and Weapons Policy Division, Ministry of Defence 1964-65; Assistant Chief of the Naval Staff (Policy) 1968-69; Flag Officer, Second-in-Command, Far East Fleet 1969-70; Vice-Chief of the Naval Staff 1971-73; C-in-C, Fleet 1973-75; KCB 1973; C-in-C, Naval Home Command 1975-77; Flag ADC to the Queen 1975-77, First and Principal ADC 1977-79; GCB 1976; Chief of the Naval Staff and First Sea Lord 1977-79; Chief of the Defence Staff 1979-82; created 1982 Baron Lewin; KG 1983; President, Shipwrecked Fishermen and Mariners' Royal Benevolent Association 1984-95; Chairman, Trustees, National Maritime Museum 1987-95; married 1944 Jane Branch-Evans (two sons, one daughter); died Woodbridge, Suffolk 23 January 1999.