Abstract: An essentially non-compressible cartesian toy submarine is provided which, when submersed in a liquid confined within a pressurized vessel, has the ability to ascend, descend and travel in a lateral plane in response to minor variations in pressure imposed within the vessel. The toy is comprised of a hull having a streamlined bow and a vertically tapered stern. An air-holding chamber, centrally positioned on the upper portion of the hull, has an aperture in its lowermost portion located within the hull. A channel extends through the rear portion of the hull, communicating with said air-holding chamber and the exterior of said hull. The channel is preferably straight and angled downwardly and sidewardly with respect to the longitudinal axis of the hull.