The raid on Pearl Harbor in December 1941 made every naval installation fearful of enemy attacks. Charlestown installed anti-aircraft batteries on roofs and camouflaged waterfront buildings. Some security measures were disruptive of yard routine. Blackouts and dim-outs were in force, especially in the early years of the war, to reduce the chances of ships being silhouetted against lights. When the air raid whistle blew, workers had to stop what they were doing and go to shelters. Throughout the war, yard officials juggled the conflicting demands of security and production. Other security measures had more personal consequences. Some yard workers were banned from certain areas, and everyone was forbidden to speak foreign languages while at work. A number of workers were suspended in 1941 as security risks. “Remarks ... inimical to the government” were enough to earn an employee a place on the suspension list. The huge number of people working at Charlestown was another sign that the yard had been remade by war. The U.S. Navy became the world’s largest single employer of industrial labor during the conflict, and the Charlestown yard held the same status in the Boston area. The yard’s force rapidly swelled from 5,000 workers in 1939 to a high of about 50,000 at Charlestown and its annexes in mid-1943, working around the clock in three eight-hour shifts. As in World War I, the yard again had to protect its essential employees from the draft board. But voluntary enlistment proved to be the real drain on the workforce. Although yard foremen tried to dissuade crucial employees from going, some 13,000 workers left the yard to join the fight. Throughout the conflict, even when more than 50,000 people worked there, the yard was shorthanded. Mainstays of the Yard: Warship Overhaul and Repair After the construction boom created by World War II, Charlestown resumed its traditional role of “serving the fleet” (the yard’s motto). In the early 1950s it was the home yard for 121 vessels, including U.S.S. _Cassin Young_, the destroyer now on exhibit at the yard. All types of ships, but especially destroyers, came for everything from minor repairs to overhauls on established cycles. The latter, which often involved some degree of modernization, could require 800 to 900 workers a day. After the war the yard preserved decommissioned vessels of the Atlantic Reserve Fleet berthed at the South Boston Annex. Charlestown also prepared ships for transfer to allies, outfitted vessels built elsewhere, and repaired equipment, especially sonar. [Illustration: U.S.S. Wasp plaque] [Illustration: _Charlestown was busy in 1960 with overhauls and modernizations. In the foreground: aircraft carrier_ Wasp _(whose crew presented the yard with the plaque shown above); floating dry dock (in a yard dry dock); heavy cruiser_ Macon (_CA-132_).]