Development of the spectrophotometer also had direct relevance to the war effort. For example, the role of vitamins in health was being studied, and scientists wanted to identify Vitamin A-rich foods to keep soldiers healthy. Previous methods involved feeding rats for several weeks, then performing a biopsy to estimate Vitamin A levels. The DU spectrophotometer yielded better results in a matter of minutes. The DU spectrophotometer was also an important tool for scientists studying and producing the new wonder drug penicillin. By the end of the war, American pharmaceutical companies were producing 650 billion units of penicillin each month. Much of the work done in this area during World War II was kept secret until after the war.