Updated I made a larger cavity to allow for more weight in the torpedo bottom (Torpedo Bottom V2)as it appears based on individual materials and settings the torpedo may be too buoyant.

This is a small torpedo shaped toy that you throw in the pool and retrieve from the bottom. The torpedo is two pieces, you load the top of the bottom half with BB's to weigh it down then screw down the top. I used #4 sheet metal screws .375" long to attach the top. The body is PLA and the top is PETG for impact strength. The fins allow it to spin as it goes to the bottom of the pool.