The United States is facing increasing international pressure to place limitations on the use of military sonar ... that has been linked to mass strandings of whales. The European Union Parliament -- the most prominent of four international bodies that have taken up the matter in recent months -- called in October for its member states to develop a moratorium on all types of military sonars, which use powerful sound to locate objects such as submarines. According to studies cited by the EU and the other world bodies, noise can interfere with the survival of the ocean creatures that depend on sound to navigate, find food, locate mates, avoid predators and communicate with one another. At high decibel levels, noise can kill. The U.S. Navy is the biggest user of midfrequency active sonar in the world -- and government officials have been loath to require permits to regulate its use. In more than a dozen instances dating back to the 1960s, however, whales have stranded themselves on the beaches and sometimes died at the time of naval training exercises miles away using midfrequency active sonar. An unprecedented stranding of 16 beaked and minke whales in the Bahamas in 2000 brought worldwide attention to military sonar. A NOAA investigation concluded that a Navy testing maneuver using midfrequency sonar -- by far the most commonly used type of sonar -- was the likely cause. Necropsies found signs of brain hemorrhaging, which is consistent with injury from sound.