Previous submersible craft all use variable weight and or displacement (ie ballast and buoyancy tanks, drop weights, etc.) to change their apparent weight in water causing the craft to either sink or become buoyant and rise to the surface. Variable Buoyancy (VB) is then a fundamental characteristic of the bathyscaphe, submersible, and submarines. In contrast, Deep Flight I has no VB systems; rather it moves vertically through the water, under power using forces developed on its wing surfaces similar to an aircraft. Deep Flight I makes an analogous transition underwater that balloons/blimps made in air to heavier than air machines, or fixed wing aircraft.