found wide spread applicability in reducing noise or the damaging effect of shock waves in a variety of industry from: underwater blasting, to pile driving, to explosive metal forming. Principle of operation The Masker portion of the system is based upon creating a speed of sound (acoustic impedance) mismatch between the bubble curtain and the seawater. Acoustic waves encountering material with a radically different speed of sound do not penetrate, but are reflected back. The speed of sound in a medium is dependent upon the square root of stiffness of a material divided by its density. In a bubble cloud, the density is most similar to that of the water, but the stiffness is that of air. The result is that the speed of sound is almost ten times slower through a cloud of bubbles in water than in water itself, and is three times slower than the speed of sound in air. Thus, sounds within the ship (or submarine) hull which would otherwise go out into the water and propagate for a long distance are reflected back into the hull and are eventually dissipated. One can experience a manifestation of these physics concepts by filling one glass with water, a second glass with carbonated water, and tapping the side of each with a spoon. The water-filled vessel will ring. The vessel with bubbles in it will "thud". The noise quieting of the Prairie screw works on a different principle. The principal noise problem with a screw is cavitation. The pressure behind the moving blade may become so low that it is less than the vapor pressure of water at that depth. This results in a water vapor bubble forming. When the bubble gets out of the low pressure area, it collapses right back into water and makes a loud noise in doing so. If, however, the trailing edge of the screw emits a small amount of air, then the cavitation bubbles have a bit of air within them. The collapse of the water vapor does not completely close the bubble, and thus little extra noise is generated. Masker The Masker portion of the system is designed to silence a vessel's engine noise from detection by threat vessels and to reduce self-noise to increase the vessel's own sonar efficiency. The Masker portion typically consists of two bands fitted to the outside of the hull adjacent the vessel's engine rooms, compressed