TAMIYA America, Inc Extra-Thin Cement, TAM87038

This is what you want: https://a.co/d/0c93M4dq

Lots of ships and sub models of various different sizes and prices! They require assembly, all you need is a bottle of Tamiya extra thin cement and a simple tool kit. You might want to put some ballast in it too. You can go crazy spending months building one to a high level but if you just want something to play with in the pool you can put it together in an afternoon.