When Argentina’s military junta invaded the Falkland Islands, a British colony, in April 1982, Margaret Thatcher’s political future was in serious question.

Britain's first female prime minister was facing sharp criticism from both her cabinet and the public in response to her domestic policies. Savage government spending cuts, a declining manufacturing industry and high unemployment all pointed to an early exit for the leader.

“It began to look as if the lady who said she was ‘Not for Turning’ would have to do a U-turn, halt her deflationary economic policies, and pump money back into the economy,” says Victor Bailey, a former distinguished professor of modern British history at the University of Kansas and former director of the Joyce & Elizabeth Hall Center for the Humanities. “The Falklands War saved her political skin. She could show all her indomitable will in a single cause with moral clarity: saving the Falkland Islanders and their sheep from the rampaging Argentinians.”

Thatcher’s decision to go to war to recover the islands was at odds with several members of Parliament and close advisers, as well as U.S. President Ronald Reagan, who repeatedly urged peace talks.

"When you are at war you cannot allow the difficulties to dominate your thinking: you have to set out with an iron will to overcome them," Thatcher writes in Downing Street Years, her 1993 memoir. ''And anyway what was the alternative? That a common or garden dictator should rule over the queen's subjects and prevail by fraud and violence? Not while I was prime minister."

Under Thatcher’s leadership, on April 5, 1982, the British government sent a naval task force 8,000 miles into the South Atlantic to take on the Argentine forces in advance of an amphibious assault on the islands. The British fleet ultimately included 38 warships, 77 auxiliary vessel and 11,000 soldiers, sailors and marines.

“We must recover the Falkland islands for Britain and for the people who live there who are of British stock,” Thatcher said in an April 5, 1982 interview with ITN.

The conflict lasted 74 days and ended with the Argentine surrender on June 14, 1982. In the end, 649 Argentine military personnel, 255 British troops and three Falkland Islanders were killed in the conflict that returned the islands to British control.

According to Bailey, Thatcher “did what [Winston] Churchill had a bad habit of not doing, which was she gave overall command to her military leaders and did not interfere with their strategic decisions.”

Her quick response to the South Atlantic conflict and swift victory led to a surge in her popularity and subsequent reelection in 1983. She would go on to serve until 1990, making her Britain’s longest-serving prime minister of the 20th century.

“She was decisive, determined, effective,” says historian Chris Collins of the Margaret Thatcher Foundation. “There was never the slightest note of doubt in her public responses, and she was pretty clear privately too. We would get the islands back. I don't think any other British leader at that time would have handled things quite as clearly.”

Above all, Collins adds, the events of the war vindicated her. “If the war had been lost, or there had been some messy or ambiguous outcome, it would have destroyed her,” he says. “But a swift decisive victory was essential, really, from her point of view.”

The triumph also proved Thatcher’s “Iron Lady” moniker was deserved.

“Before the Falklands it was a bit of a joke, that phrase,” he says. “Afterwards it meant something quite real. She was seen as enormously tough and resourceful, someone you would not take on if you were wise.”

And, Bailey notes, Thatcher was the first woman to lead the country into battle since Elizabeth I.

“I’m sure she liked this fact,” he says. “It was rare in the modern day for politicians to have an international conflict to handle—the last one for England had been Suez in 1956. It gave Thatcher an international stage to perform upon. … In a way, it elevated her from being a national politician to being an international stateswoman. As the first female prime minister of Britain, her success probably helped to make the idea of a female leader more acceptable.”

The public, Bailey says, felt Thatcher had “restored the ‘Great’ in Great Britain; she had elevated the confidence of the nation. We could still sail halfway round the world and succeed militarily.”

But it wasn’t just the public who recognized the change in Thatcher’s leadership, according to Collins.

“She genuinely gained enormously in confidence and stature," he says, "and it stayed with her."