In August 1943, Eleanor Roosevelt set out in secret for the Pacific theater, where the United States and other Allied forces were battling Japan. At a San Francisco-area Army airfield, she boarded a military transport plane, sharing space with supplies and sacks of mail. Nearing midnight, the aircraft took off, bearing the First Lady into a theater of war unlike any other in history—a watery expanse described by Life magazine as “the vastest single battlefield over which man has ever fought.”

What followed was a feat of bravery and endurance. Even for a First Lady who continually pushed boundaries, it was the most extraordinary undertaking of an unconventional and dramatic career.

In five weeks, Eleanor logged some 25,000 miles, a distance roughly equal to the Earth’s circumference. She trekked to Hawaii, New Zealand, and Australia, and through the South Pacific. Her ultimate destination was the island of Guadalcanal, the site of the first major Allied offensive of the Pacific war and which was still under enemy air attack.

Due to security concerns, Eleanor’s whereabouts were kept under wraps for the first 10 days of the trip as she island-hopped through the South Pacific visiting military outposts.

Her first inspection stop was Christmas Island, a link in the chain of island bases along the supply and communications route connecting the United States with Australia and a speck of land so tiny she wondered why a robust wave didn’t wash it away.

The soldiers stationed on Christmas Island noticed heightened security measures being put into place, and they speculated that someone important was coming their way. They were expecting a V.I.P., and yet they were astounded when Eleanor Roosevelt stepped off the plane.

On Christmas Island, Eleanor set the rigorous pace she would keep throughout the trip, during which she inspected everything from artillery headquarters to a dentist’s tent in the Australian outback. She slept on Army cots in rustic huts, traveled by jeep over rough terrain to reach isolated camps, and tramped through the jungle on a simulated training exercise to better understand jungle warfare.

Eleanor seized every opportunity to speak with servicemen, often rising at dawn to breakfast in mess halls. And she walked miles of hospital wards, going bed-to-bed comforting the wounded. She reported her findings to the president directly and to the American people through her six-day-a-week, syndicated newspaper column, “My Day.”

By the time Eleanor set out for the Pacific, she had been First Lady for a decade. She was famous for her travels, or infamous depending on the perspective, and she constantly made headlines for them.

Traditionally, First Ladies were discreet figures in the presidential background, primarily overseeing social functions and taking no active part in public life. But Eleanor, an avid flyer who first took to the skies in 1929 and wanted to be a pilot herself, refused to be grounded at the White House.

Instead she created for herself a unique role that combined her wanderlust with her sense of social responsibility. She ceaselessly crisscrossed the country inspecting New Deal initiatives and seeing and meeting people, using the information she gathered to exact change through her own means or by providing it to the president and his policy advisers.

As First Lady she averaged an astounding 40,000 miles on the road each year, including a 1934 trip to Puerto Rico to investigate labor and living conditions at the president’s behest. The fact that she flew over water to get there cemented her reputation as fearless and unconventional.

Controversy over Eleanor’s travels was still going strong in 1943. The Pacific trip far exceeded anything she had previously done, including a wartime visit to Great Britain the year before. Once news broke that she had turned up on the other side of the world, it generated an onslaught of media coverage. Everyone from politicians to newspaper editors to ordinary citizens seemingly had an opinion about it and took sides for and against Eleanor and the trip.

The intense spotlight worked to Eleanor’s advantage, expanding her voice and her wartime leadership even further. Throughout World War II, she used “My Day” and her numerous other platforms to guide the nation, buoying morale and admonishing when necessary, such as chastising Americans for believing enemy propaganda.

Now, she drove home hard truths to the American public. She warned against the complacency she saw beginning to take root on the home front, including strikes at war production factories, which jeopardized the lives of the fighting men.

She brought public pressure to bear on Congress, pushing for legislation to support veterans. She also used the limelight to continue to advocate for causes she had long championed—racial equality and integrating the armed forces, as well as women’s greater involvement in civic life.

Perhaps most important, Eleanor impressed upon the world the need to “lay a better foundation for peace than we did the last time,” as she stated during a speech in Wellington. The vast numbers of young men she met in hospitals in the Pacific, who would forever carry with them the results of the war, haunted her and reinforced her determination to see the war through and to maintain peace.

Eleanor’s presence on the global stage during World War II preceded an even greater worldwide role. While she was in Rockhampton, Australia, the town’s mayor declared that he “would like to see Mrs. Roosevelt at the peace conference table” and that he was sure it was a widely held opinion.

His words proved prescient. In December 1945, Eleanor was appointed by President Harry S. Truman to the first United Nations delegation, the only woman among the delegates.

During the dozen years Eleanor spent as First Lady, upending tradition and breaking new ground, her journey to the frontlines most powerfully illustrated how dramatically she transformed the role. A reporter at the time described Eleanor’s trip to the Pacific as “the most remarkable journey any president’s wife has ever made.” An assertion that still stands eight decades on.