A submersible vehicle having an outer hull which defines a hull axis and appears substantially annular when viewed along the hull axis, the interior of the annulus defining a duct which is open at both ends so that when the vehicle is submerged in a liquid, the liquid floods the duct. The vehicle further comprising means for rolling the vehicle about the hull axis. A buoyancy control system may be provided, and the outer hull may be swept with respect to the hull axis. Various methods of deploying and using the vehicle are described.