to a 24-hour schedule. The submarine force has always been a small fraction of the active Navy. During World War II all submariners (including the rear echelon) accounted for less than two percent of Navy personnel, but accounted for 55 percent of Japan's merchant marine losses. In 1998 only about seven percent of the Navy's people were submariners, though they operated one-third of the Navy's warships. Training After acceptance into the submarine program, candidates undergo a demanding training schedule, which includes attendance by all Officers and non-nuclear trained enlisted personnel at the U.S. Naval Submarine School New London, located within the Naval Submarine Base New London, in Groton, Connecticut, (NAVSUBSCOL at SUBASENLON) as well as rigorous technical training in different specialty areas. Officer and enlisted engineering staff have their own advanced training at Nuclear Power School in Charleston, South Carolina, then nuclear prototype training at various locations. Besides their academic and technical training, much of which is Classified Secret or Top Secret, all prospective US Naval Submariners, both officers and enlisted personnel, undergo 3 phases of physical training and testing related to the intense pressure differential between the surface and submarine operating depth. Pressure training Pressure training is conducted in a 2-day course including classroom and lab training: The first test is for the ability to perform the Valsalva maneuver, named for Antonio Maria Valsalva. If a submarine training candidate cannot perform the Valsalva maneuver under doctor's supervision at normal atmospheric pressure, that candidate is not rejected as unfit for submarine service but may not continue the high risk pressure training as follows. In the second phase of testing, called Pressure Testing, candidates who have successfully performed the Valsalva maneuver will be subjected to increased ambient pressure. This test is performed under the supervision of a diving-certified medical doctor. All testees enter a pressure chamber, accompanied by the doctor, and the 'tank' is sealed. Typically, there is in the chamber a somewhat surprising object: an inflated volleyball, water polo ball or similar inflated ball. Upon sealing the tank, pressure is increased, while the testees equalise their eardrum pressure. (if any testee is unable to 'Valsalva', the test stops, and pressure is slowly released.) Pressure builds within the chamber until the chamber is equal to water pressure at "escape depth". At this point, the chamber feels very warm and dry, and the volleyball has become compressed enough that it has become