The beginning of World War II in Europe and the threat of the U.S. becoming involved generated new jobs in defense-related industries. After the U.S. became involved in the war in 1941, the city mobilized. Philadelphia consistently met war bond quotas and when the war ended in 1945, 183,850 residents were in the U.S. armed forces. With so many men serving in the military, there had been a labor shortage; businesses and industries hired women and workers from outside the city. In 1944, the Philadelphia Transportation Company promoted African Americans to positions as motormen and conductors (from which they had previously been excluded) on public transportation vehicles. Resentful, other PTC workers protested and began a strike that nearly immobilized the city. President Roosevelt sent troops to replace the striking workers. After a federal ultimatum, the workers returned after six days.