The U.S. is selling Egypt a towed array sonar system, for $23 million. The three ton LFATS (Low Frequency Active Towed Sonar) system is compact and can be carried by small warships (large patrol boats or corvettes) and is very good at finding quiet submarines in shallow coastal waters. Egypt plans to equip its Chinese made patrol boats with the new system.
Although a defense system, sometimes towed arrays can have offensive use. In June, 2009, an American destroyer, while training off Subic Bay in the Philippines, had its towed sonar array collide with a Chinese submarine. The U.S. Navy did not reveal if the American ship had detected the sub before the collision. If the array was not activated, its sound (sonar) detectors would not have detected the sub. The Chinese admitted the sub was one of theirs, and the boat was apparently following the American ship unaware that a sonar array (which usually operates over a hundred meters beneath the surface, and up to two kilometers behind the ship towing it) was there.