Read the passage.

Harriet Tubman's Unsung Heroism
Harriet Tubman is famous for her role as a "conductor" on the Underground Railroad. While her work as a scout and spy for the Union Army during the Civil War is not as well known, it is no less heroic. One of her most important military successes occurred when Union forces were preparing to raid a Confederate-held area along the Combahee River and destroy the South's supply routes. The Confederate Army had hidden mines throughout the waters, endangering the Union soldiers, but Tubman found a way to bypass this hazard. Knowing that the mines had been placed by enslaved people forced to work for the Confederates, she led a secret mission into enemy territory and convinced the enslaved workers to divulge the mines' locations. Armed with this information, Tubman was then able to guide Union gunboats safely past the mines during the raid. The Union soldiers not only successfully raided the Confederate supplies but also freed more than 700 enslaved people along the way.
What is the main, or central, idea of the passage?

The main idea of the passage is the unsung heroism of Harriet Tubman, particularly highlighting her less well-known role as a scout and spy for the Union Army during the Civil War.

The main, or central, idea of the passage is that Harriet Tubman's role as a scout and spy for the Union Army during the Civil War was heroic and led to important military successes, such as the raid on the Confederate-held area along the Combahee River.