Prairie-Masker

Prairie-Masker is a radiated noise reduction system fitted to some[clarification needed] western warships, including the Oliver Hazard Perry-class frigates, Spruance and Arleigh Burke-class destroyers, and the Ticonderoga-class cruisers of the US Navy.

The system was also installed during the 1960s on a limited number of post WWII Guppy III modified, and later diesel submarines.

[1] The Masker and Prairie systems are designed to prevent the classification or identification of a warship's acoustic signature by another vessel, i.e. by a hostile submarine.

[2] The use of air-bubbles and their effects upon acoustic wave propagation began to be studied systematically during the Second World War as part of a general effort to understand sound in submarine warfare.

Results of that study most pertinent to this discussion are found in Part IV of that volume Acoustic Properties of Wakes.

[3]: 347 The Masker portion of the system is based upon creating a speed of sound (acoustic impedance) mismatch between the bubble curtain and the seawater.

When the bubble gets out of the low pressure area, it collapses right back into water and makes a loud noise in doing so.

On submarine installations this was prevented by running a trickle of fresh water through the system when the ship was in port.

A similar system called Agouti was fitted to Royal Navy frigates and such vessels as INS Nilgiri.