Many people have heard about how Alexander Fleming, a Scottish bacterialist, discovered penicillin, the first antibiotic, in the 1920s. This was a huge development: For most of history, bacterial infections caused 40%-50% of deaths worldwide. Today, thanks to the invention of antibiotics, this number has been lowered significantly.

Less widely known, though, is the fact that it took a long time, a World War II collaboration, and U.S. federal funding to figure out how to make penicillin in the very large quantities needed. Developing that know-how was a critical step towards making antibiotics the mercifully common medicine they are now.

Fleming himself was unable to make penicillin in large quantities. Other British scientists joined the effort. The Second World War, with its many wounded and the many consequent infections, made large-scale penicillin production particularly urgent. But the war itself made it difficult to carry out the research in Britain. So, scientists from Britain teamed up with scientists in the U.S Agriculture Department Northern Regional Research Laboratory, in Peoria, Illinois, to work together to find a way to industrialize penicillin production.

They developed a new method of bacterial production known as deep-tank fermentation. It involves first growing a culture of Penicillium, the bacteria that produces penicillin, and then transporting that culture into a large vat of nutrient broth solution. The hope was that the bacteria would go wild in their nutrient bath and multiply massively throughout the large vat. The scientists experimented to fine-tune the broth, aerating it to make sure the bacteria had the oxygen they need to grow, changing the sugar used in the broth, adding amino acids (which are the building blocks of all proteins, including the proteins bacteria are made of), and adding corn-steep liquor, a byproduct of corn processing that bacteria turn out to find particularly yummy and nutritious. By the time they had finished their fine-tuning efforts they had increased penicillin yields 10 to 12 times over.

With this critical step in hand, the USDA’s Northern Regional Laboratory also collaborated with pharmaceutical companies, and through this broad-based collaboration, by 1943 it became possible to mass-produce penicillin. Just in time. The first major test of penicillin’s mettle came only a year later, in events that began on the 6th of June, 1944: D-Day, the beginning of the Allied invasion to liberate mainland Europe. With many soldiers injured that day, penicillin was prescribed en masse. It has been estimated that it reduced D-Day mortality rates by 15%. Penicillin has since saved millions of other lives, and it became the starting point for the development of many other life-saving antibiotics.