Complex sentence: Initially, only "elite, especially reliable German workers" were allowed to work in the arms industry, but with the outbreak of World War II in 1939 and many men entering the Wehrmacht and Luftwaffe, workers became harder to find.
Split into simpler sentences: Initially, only "elite, especially reliable German workers" were allowed to work in the arms industry. However, with the outbreak of World War II in 1939 and many men entering the Wehrmacht and Luftwaffe, workers became harder to find.