A submersible , or bathyscaphe, is a type of unerwater vessel with limited mobility which is typically transported to its area of operation by a surface vessel or large submarine. Apart from size, the technical difference between a 'submersible' and a 'submarine' is that submersibles are not totally autonomous. They may rely on a support facility or vessel for charging of batteries, high pressure air, high pressure oxygen replenishment, or all of these. The main problem with submersibles is that they may be relatively small, holding only a small crew.