THERE ARE TEN PROHIBITED SUBJECTS
1. Don't write military information of Army units -- their location, strength,, materiel, or equipment.
2. Don't write of military installations.
3. Don't write of transportation facilities.
4. Don't write of convoys, their routes, ports (including ports of embarkation and disembarkation), time en route, naval protection, or war incidents occurring en route.
5. Don't disclose movements of ships, naval or merchant, troops, or aircraft.
6. Don't mention plans and forecasts or orders for future operations, whether known or just your guess.
7. Don't write about the effect of enemy operations.
8. Don't tell of any casualty until released by proper authority (The Adjutant General) and then only by using the full name of the casualty.
9. Don't attempt to formulate or use a code system, cipher, or shorthand, or any other means to conceal the true meaning of your letter. Violations of this regulation will result in severe punishment.
10. Don't give your location in any way except as authorized by proper authority. Be sure nothing you write about discloses a more specific location than the one authorized.