1920s but reacted with extreme militancy to the hardships of the depression. Following the success of the sit down strikes at General Motors, non-unionized, semi-skilled workers followed suit in numerous plants in 1937. They were supported by the pro-union mood of the city, the New Deal's permissive political climate, and Governor Frank Murphy's pro-labor sympathies. They won many concessions and formed numerous locals outside the auto industry. Ford, however, successfully resisted unions until 1941. World War II and the "Arsenal of Democracy" The entry of the United States into World War II brought tremendous changes to the city. From 1942 to 1945, production of commercial automobiles in the city ceased entirely, as its factories were used instead to construct M5 tanks, jeeps, and B-24 bombers for the Allies. The Guardian Building was converted into a headquarters for wartime production. The city made a major contribution to the Allied war effort as part of America's Arsenal of Democracy. Historians note that this accolade was "easily and often corrupted to 'arsehole'" by tired Detroiters waiting in lines everywhere. The government believed that Detroit was vulnerable to air attack, and encouraged companies to diversify production to outside the region. The B-24 Liberator, the most produced bomber in history, was used to bomb Germany heavily. Before the war, the aviation industry could produce, optimally, one such plane a day at an aircraft plant. By 1943, Ford's plants managed to produce one B-24 an hour at a peak of 600 per month in 24-hour shifts. Many pilots slept on cots waiting for takeoff as the B-24 rolled off the assembly line at Ford's Willow Run facility. Detroit's wartime manufacturing boom coincided with the decline of Southern agriculture, attracting hundreds of thousands of Southern Blacks to the city in search of economic security and freedom from racist Jim Crow laws. The ongoing draft pillaged Detroit's industrial labor supply, leaving a labor shortage so dire that former auto plants had no choice but to hire Black workers. According to a 1944 report, "a 44% advance in wartime employment brought with it an advance of 103% in the total number of Negroes employed". As Detroit's Black population continued to increase, housing options grew distressingly scarce. Unscrupulous landlords took advantage of the influx of Black workers and limited housing supply, gouging monthly rent prices in Black neighborhoods. In some cases, Black tenants paid "20 to 40 percent more for