Following the outbreak of World War II in 1939, Admiral Ernest King led a board to evaluate anti-aircraft defenses of the fleet's ships, and it recommended adding blisters to restore freeboard, the adoption of 5 in /38 cal. dual-purpose guns, and a strengthening of the ships' decks. The Chief of Naval Operations decided that, as a result of the likelihood of war, only the bulges would be fitted, and "West Virginia" was slated to undergo the work from 10 May to 8 August 1941, though the modification was not carried out. The Navy conducted the final iteration of the series, Fleet Problem XXI, in April 1940, by which time tensions with Japan over the latter's initiation of the Second Sino-Japanese War had led the United States to transfer the fleet from California to Pearl Harbor in Hawaii as a deterrent to further aggression by Japan. The fleet spent 1941 occupied with extensive training to prepare for the anticipated war with Japan, even after the diplomatic situation increasingly worsened in the final months of the year. During this period, the Navy sought to improve the anti-aircraft batteries of the fleet's battleships, but production of the new guns was slow, so old 3 in guns were reinstalled as a temporary measure. The ship also had eleven .50-cal. machine guns by this time. In June, men aboard "West Virginia" fabricated an experimental gun shield for the 5 in guns, which were to be applied to other ships. "West Virginia" was to have had her 1.1 in guns installed in February 1942.