This is one of the mid sized Keystone subs it is not as large as the U-18’s but much larger than the S3’s. It measures 14″ x 2.5″. There is only one torpedo tube and it is smaller than the U-18’s. The projectile it fires is the same that is used with any of the ships. I have seen a few of these but cannot specifically date it yet. The sub does not appear in any of the catalogs prior to 1943 or after 1951 so at this point I would say late 1940’s.
From my private collection.