In the last scene Dennis (Jay North) says; 'I can't wait to get old a join...the Navy'. In reality Jay North did join the Navy in later life.
He served in the U.S. Navy (1/16/1977-8/10/1979). He was a seaman stationed in Norfolk, Virginia. He did a lot of manual labor and left with an honorable discharge.
The submarine is the USS Trepang (SS-412), a Balao-class attack sub, it was the first ship of the United States Navy to be named for the Trepang, (Holothuroidea), which is a marine animal having a long, tough, muscular body, sometimes called a 'sea slug' or a 'sea cucumber', found on coral reefs.