This was a form of mail used during the war to save space and supposedly to get letters home sooner. They came in two forms, cards for special events like Father's Day, and in a blank letter format. This particular card was used for Father's Day in June 1945.
The original was censored, then photographed. The film was sent to the U.S. where a photographic copy was made and then put in the regular mail for delivery to the recipient.
Should relate a funny (?) story on myself. Being part of the "silent service", we were not allowed to tell where we were or what we were doing. That doesn't leave much to say. We were, however, "required" to send a letter home. It seems that when the censor, an officer on the boat assigned to that duty, got finished cutting out everything not allowed, not much was left. Rather than write something and have it cut out by the censor, I thought I'd be a clever one and do the cutting myself. I started out with "Dear Mom", and then proceeded to cut out rectangles (like paragraphs) to the bottom of the page. Signed it: "Love from your son, Frank". The officer sent for me, chewed me out, and directed that I sit down right there and compose another letter.....without the holes!