Her quasi-memoir Scenes in the Life of Harriet Tubman (told to Sarah Bradford and written in the third person) explains how things worked. While African Americans were suspicious — often rightly — of Union soldiers, they were willing to trust Tubman. “To Harriet they would tell anything,” Bradford writes. “It became quite important that she should accompany expeditions going up the rivers, or into unexplored parts of the country, to control and get information from those whom they took with them as guides.”

Tubman was one of the most valuable field-intelligence assets the Union Army had. She had hundreds of intelligence contacts and could establish new ones — particularly among African Americans — when nobody else could.

During one of her scouting missions along the Combahee River, she became the first woman and one of the first African Americans to command a significant number of U.S. troops in combat. The raid she organized and helped to command freed far more enslaved people than her decades of work on the Underground Railroad. She also was a strong advocate of allowing African Americans into the Union Army. She knew Robert Gould Shaw, who commanded the almost entirely African-American 54th Massachusetts Volunteer Infantry regiment — the unit at the center of the 1989 film Glory. A (probably apocryphal) legend even has it that she cooked his last meal before the heroic assault in which he and much of his regiment perished.

In her “retirement” — she never really stopped working until she became ill at the very end of her life — Tubman remained a political presence. A friend of Secretary of State William H. Seward, she settled in his hometown of Auburn, N.Y., on land he sold her. There, she helped to build both a church (she was devoutly religious) and a privately run retirement home. She also fought for women’s suffrage, supported Republican politicians, and advocated for fair treatment of black Civil War veterans, which they rarely received.