Oklahoma_hand_stamp.jpg
"To record when a piece of mail was processed aboard ship, the Navy used wooden postmark stamps. This one bears an ominous date: Dec 6, 1941 PM. It was recovered from the battleship Oklahoma after it was hit by several torpedoes, listed to a 45-degree angle, capsized and sank in the attack on Pearl Harbor on December 7, 1941. The Oklahoma lost 429 sailors and Marines, a third of its crew." - Smithsonian Magazine