<P> The nation went from a surplus manpower pool with high unemployment and relief in 1940 to a severe manpower shortage by 1943 . Industry realized that the Army urgently desired production of essential war materials and foodstuffs more than soldiers . (Large numbers of soldiers were not used until the invasion of Europe in summer 1944 .) In 1940--43 the Army often transferred soldiers to civilian status in the Enlisted Reserve Corps in order to increase production . Those transferred would return to work in essential industry, although they could be recalled to active duty if the Army needed them . Others were discharged if their civilian work was deemed essential . There were instances of mass releases of men to increase production in various industries . Working men who had been classified 4F or otherwise ineligible for the draft took second jobs . </P> <P> In the figure below an overview of the development of the United States labor force, the armed forces and unemployment during the war years . </P> <Table> <Tr> <Th> Year </Th> <Th> Total labor force (* 1000) </Th> <Th> Armed forces (* 1000) </Th> <Th> Unemployed (* 1000) </Th> <Th> Unemployment rate (%) </Th> </Tr> <Tr> <Td> 1939 </Td> <Td> 55,588 </Td> <Td> 370 </Td> <Td> 9,480 </Td> <Td> 17.2 </Td> </Tr> <Tr> <Td> 1940 </Td> <Td> 56,180 </Td> <Td> 540 </Td> <Td> 8,120 </Td> <Td> 14.6 </Td> </Tr> <Tr> <Td> 1941 </Td> <Td> 57,530 </Td> <Td> 1,620 </Td> <Td> 5,560 </Td> <Td> 9.9 </Td> </Tr> <Tr> <Td> 1942 </Td> <Td> 60,380 </Td> <Td> 3,970 </Td> <Td> 2,660 </Td> <Td> 4.7 </Td> </Tr> <Tr> <Td> 1943 </Td> <Td> 64,560 </Td> <Td> 9,020 </Td> <Td> 1,070 </Td> <Td> 1.9 </Td> </Tr> <Tr> <Td> 1944 </Td> <Td> 66,040 </Td> <Td> 11,410 </Td> <Td> 670 </Td> <Td> </Td> </Tr> <Tr> <Td> 1945 </Td> <Td> 65,290 </Td> <Td> 11,430 </Td> <Td> 1,040 </Td> <Td> 1.9 </Td> </Tr> <Tr> <Td> 1946 </Td> <Td> 60,970 </Td> <Td> 3,450 </Td> <Td> 2,270 </Td> <Td> 3.9 </Td> </Tr> </Table> <Tr> <Th> Year </Th> <Th> Total labor force (* 1000) </Th> <Th> Armed forces (* 1000) </Th> <Th> Unemployed (* 1000) </Th> <Th> Unemployment rate (%) </Th> </Tr>

What was the main way that business leaders helped the war effort during world war ii