The original Terrier plans indicate how to make torpedo tubes and a gun position from paper and paperclips. I don't have the plans, but the method is shown below
Cut a sheet of A4 into strips. One is 5/8" wide, one is 1/8" wide, and one is 1/4" wide. Snip off two sections of paperclip wire with a half a curve as shown - about 3/4" long in total. That's about it!
You guessed it! Wrap the 5/8" strip round a 3/4" former, and glue it.
The 1/8" strip goes to make a reinforcing ledge at the top of the tub.
Wrap the 1/4" strip of paper round one of the wires as shown, and glue after about 5 turns...