Throughout the history of military conflict, officials in the U.S. armed forces have deemed it necessary to monitor and censor correspondence from soldiers at war. This practice began during the Civil War, mainly when mail had to cross enemy lines, but it wasn’t heavily used until World War I.

During World War I and II, censors generally looked for two things: anything that would be of value to the enemy (location, troop strength, etc.) or a weakening of morale. Some letters were also confiscated because they used graphic language or mentioned sex. Letters in foreign languages were also usually intercepted.

Usually officers were the individuals responsible for doing the censoring, but it became an unpopular job and was sometimes left to the chaplain or dentist in a unit.

If only sections of a letter need to be censored, they would be cut or blacked out with ink. Often however, entire letters were confiscated and not returned to the soldier. If the military used special chemicals to check for invisible writing, something that was done when a spy was suspected, the letter would be destroyed so that the practice did not become common knowledge.

Historians believe that censorship influenced the quality of letters written. In general, in the Revolutionary War and the Civil War letters had much more information, especially describing location. Letters written during the Korean War and the Vietnam War, once censorship was less stringent, also contained much more colorful descriptions of battle.

Today, the United States military is again debating over the need for censorship, especially of e-mails sent by soldiers in war zones.