My sources were Arthur Herman’s excellent history of the Royal Navy and John Nott’s entertaining memoir, “Here Today, Gone Tomorrow.” But I have now pulled The Downing Street Years off the shelf, where on pages 178-9, the Leaderene herself gives us the following timeline:
March 28: Mrs Thatcher, in Brussels, talks to Foreign Secretary Lord Carrington and they agree to send a nuclear submarine to show the Argentines we mean business
March 30: Back from Brussels, but Peter Carrington has gone to Israel.
March 31: Intelligence initially says that Argentina will stop short of full-scale invasion. That evening, Nott calls an urgent meeting, as Argentina has launched an invasion fleet. The MOD does say that the Falklands could not be retaken. Mrs T replies, “If they are invaded, we have to get them back.” At this point, Leach enters (although Thatcher says in civilian dress, which contradicts Nott’s account). Mrs T gives him the authority he seeks.
She sums up: “Before this, I had been outraged and determined. Now my outrage and determination were matched by a sense of relief and confidence. Henry Leach had shown me that if it came to a fight, the courage and professionalism of Britain’s armed forces would win through.”
Nott, meanwhile, says (p.258), “[Leach’s intervention] greatly boosted the confidence of Margaret Thatcher; it was met by some scepticism among the rest of us.”
In other words, while Mrs Thatcher had the determination, it was Leach who gave her the means to carry through her determination to victory over Nott (an admirable man, actually, and one of my political heroes) and the other Chiefs of Staff at that very first meeting.