A submersible surface-planing vessel has the capability to operate with a lowered profile on surface propulsion to lessen the visibility of the vessel, and sink to the bottom for temporary storage, followed by resurfacing and dewatering to operate as a planing craft. Surface propulsion is provided by an engine system which can be totally sealed when the vessel submerges. A buoyancy system, which may include both open and closed ballast tanks, permit the vessel to sink, refloat or to be of neutral buoyancy as required. The vessel is constructed to maintain the center of buoyancy above the vessel's center of gravity irrespective of the degree of fill of the ballast tanks to maintain the vessel in an upright orientation at all times when under water and transitioning between surface and submerged states.