I believe Richard Feynman had the same problem when he sent letters home to his girlfriend from Los Alamos during WWII. The censors censored any mention of censorship because they didn't want to let on that they were working on something important enough to merit censorship... as if it wasn't obvious from the black lines through words they didn't like.

He kept trying to send her word puzzles because she liked them, but the censors wouldn't let them through, and he couldn't tell her *why* he couldn't send them.

I read the book many years ago, the reality may have been slightly different than I remember.