My grandmother has letters that my grandfather had sent her from the Pacific Theater when he was in the Army(WWII).   She has a couple that  charred!  My Grandfather said it was because the ship or plane they were carried on caught on fire from a Japanese attack most likely!  She also has ones where the writing was punched out because it gave away sensitive info(he was part of the invasion force that liberated the PI).  Pretty cool IMHO!