Those types of subs are known as dynamic divers, using the diving plains and while the sub is under speed it pulls(and pushes) the sub under the water, they are positively buoyant so stopping the ship will allow it to pop to the surface, this would be an ideal starter into subs, as long as the electronics are water tight, and the sub is postivly boyant you should have little hastle is creating one as there is no need for ballast tanks and the complicated methods of getting them working.
I would suggest if u want to do a kit bash then try Revels Gato Class Sub, while building mine, i found that the hull is built in 6 parts, and the central section u are able to screw and unscrew easy enough with a little thought.
However, if this is your first time into subs i would suggest a cheaper, easier option check out this link.
Marks Model Bits, Dynamic Diving sub!!!
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