The US passed the Espionage Act in 1917 and the Sedition Act in 1918 which put people with anti-war thoughts in jail and newspapers were shutdown.

Woman were used to get information from the enemy.

Many spies that were taken to court and porsecuted. Many were executed.

Another part of Espionage was codes, Which evolved during WWI.

Espionage was a convenient way to get intelligence from the enemy line during WWI

About Espionage: