Submarine sound emission is one of the Navy's primary concerns in maintaining operational stealth. Much of submarine noise is produced by its propulsion plant including its screw or propulsor and its nuclear driven power train. The question arises as to the feasibility of a submarine with no screw and no propulsive plant. Would it be possible to produce forward momentum by a means other than what now exists?

Airborne gliders typically have a glide ratio of about 30 feet forward for every foot lost to gravity. This is accomplished by a fixed wing with a cambered upper surface that produces at its trailing edge a partial vacuum resulting in lift. Since water is not compressible, the same concept cannot be applied to an underwater glider. However, such a submersible vessel would have an advantage in being able to use its positive and negative buoyancy to produce forward motion. A sailboat's keel or centerboard acts to resist lateral motion by its vertical placement. A similar keel or centerboard in the horizontal plane acts to resist upward and downward motion and in doing so propels the vessel forward when inclined to the horizontal.

Extending this concept it is apparent that when a winged submerged vessel is in a constant state of alternating buoyancy forward motion can be achieved. A downward angle of a wing having a negative buoyancy or the upward angle of a wing having a positive buoyancy will result in forward motion. All that is needed is a pump and tanks to achieve the out-of-neutral buoyancy. While the resulting forward motion would not be rapid it would be completely silent.

As in existing submarines, vessel angle of attack would be controlled by computerized trim tank manipulation. Of greater complexity is the problem of turning. Once again, the airborne glider acts as a limited model of reference. It uses aileron and rudder in a coordinated bank. The submersible glider could induce bank by either adjustable slots at the wing tips or by small tanks at the wing's extremities. Bank solves only half the problem. An elevator or stern plane is needed to depress the vessel's stern and it is this action combined with bank that produces a change in direction.

Since the electrical energy needed to operate the pumps has a finite life dependent on the capacity of the battery, such a vessel would need a mother submarine to replenish its energy. For this reason the vision of the submersible glider is most often considered from the view of a small satellite vessel controlled and energized from a host submarine. One scenario has the host submarine hovering or lying on the seabed while the glider performs silent scouting missions in littoral waters.

It is interesting to conceive of this possibility and the Navy is seriously investigating its potential.