As you might imagine, there were lots of spies during the Civil War. There were people who lived in the North who wanted the South to win and people in the South who wanted the North to win. This made it easy for both sides to recruit spies.
What did spies do?
Spies passed on all sorts of information regarding the armies of the enemy. They told of troop movements, numbers of soldiers, and the conditions of the enemy army. This type of information could make the difference between winning and losing a battle. It allowed generals to know when and where to attack, or if they should retreat.
What happened if a spy was caught?
Spies were treated differently than captured soldiers. Spying was especially dangerous because they were usually executed if they were caught.
Union Spy Networks
At the start of the war, the Union didn't have a very organized spy network. Although they had a lot of spies, they were usually sent out by individual generals or leaders in the government. The information wasn't communicated very well or passed on to the people who really needed it. The Union had a distinct advantage in the war as they gained a significant amount of military intelligence from the enslaved and formerly enslaved.
As the war continued, the lead generals of the North had a spymaster who would organize and gather the information from the spy network. Some of the most famous Union spymasters included Allan Pinkerton, Lafayette Baker, and George H. Sharpe.
Famous Union Spies
Sarah Edmonds - Sarah Edmonds was a master of disguise even before she became a spy for the Union. She disguised herself as a man and entered the Union army. While serving in the army she volunteered to become a spy. As a spy she used all sorts of unique disguises, pretending to be all sorts of different people from an Irish woman to a black man.
Philip Henson - Henson worked as both a scout and a spy for the Union. Henson managed to get Confederate generals to confide in him, giving him information that helped General Ulysses Grant win several battles including the Battle of Vicksburg. Henson was finally captured by the Confederates, but managed to escape near the end of the war.
Elizabeth Van Lew - Van Lew ran one of the Union's most effective spy rings out of her house near the Confederate capital city of Richmond, Virginia. She used various methods to pass secret messages to the Union including hiding them inside of baked bread, eggshells, and inside the sole of a boot.
Timothy Webster - Webster gained the trust of Confederate officials and passed on valuable documents to the Union. However, he became sick and his secret identity got out to the Confederates. They captured him and had him executed. He was the first spy to be executed during the Civil War.
Confederate Spy Networks
The Confederate spy networks were more organized than those of the North. They mostly used people who worked for the army or the government in the North, but who secretly wanted the South to win. They passed information across the border using a system called the "secret line."
Famous Confederate Spies
Belle Boyd - Belle Boyd spied from her father's hotel in Virginia. She secretly gathered information from officers and soldiers who stayed at the hotel and passed it on to the Confederacy. She was later caught, but never executed.
Rose O'Neal Greenhow - Greenhow ran a large spy ring in Washington, D.C. where she used secret codes to pass on messages to the South. She once passed important information that helped the South to win the First Battle of Bull Run in 1861. She was later captured and sent to prison for five months.
Henry Harrison - Henry Harrison spied for General James Longstreet during the war. It was information from Harrison that caused General Robert E. Lee to halt his army and prepare for the Battle of Gettysburg.