Harriet Tubman was an invaluable commander of a unit of black scouts and spies for the Union Army that operated from South Carolina to Florida. The nine-member unit made multiple trips through swamps and up rivers to gather information on Confederate Army strength and defenses and to look for slaves to enlist in the Union Army. Trained by Colonel James Montgomery, a fierce anti-slavery fighter and guerrilla warfare expert, the black troops conducted river raids with the aid of Tubman. During one raid in June of 1863, Montgomery and Tubman captured three Confederate gunboats while destroying millions of dollars' worth of stores, freeing about eight hundred slaves, and looting thousands in property.
New Orleans, Louisiana fell to the Union on April 29, 1862, after Admiral David Farragut led his fleet up the Mississippi river. They passed two poorly-guarded Confederate forts with minimal casualties in the process. The river soon belonged to the Union from New Orleans to Vicksburg, Mississippi.
"They couldn't hit an elephant at this distance."
~ Union General John Sedgwick, May 9, 1864
Just before he was shot and killed at the Battle of Spotsylvania Court House
Pauline Cushman was the only female spy who was caught and sentenced to be hanged. The day her sentence was to be carried out, Union forces routed her Confederate captors, who fled without her. President Lincoln named her an honorary major in the Union Army.