an Entity references as follows:
The Subskimmer is a Diver Propulsion Vehicle which is a form of RIB (inflatable boat) with an outboard petrol (gasoline) engine. It is equipped to inflate and deflate itself as it runs. When submerged it seals its engine and runs with battery-electric thrusters, which are on a rotatable cross-arm, and is deflated. Thus it transforms between a fast light surface boat and a submerged diver propulsion vehicle. The central box contains the pump to deflate and inflate the tubes, and miscellaneous kit. The batteries, being heavy, are in a thick tube along its keel. Its outboard motor has a long snorkel so the Subskimmer can run on motor just submerged to try to avoid detection. Its thrusters are on a rotatable cross-arm which contains navigation kit.