Complex sentence: These skills were applied to the mass production of the antibiotic penicillin during World War II in response to the need of the U.S. government to treat injured Allied soldiers; most of the penicillin that went ashore with the troops on D-Day was made by Pfizer.
Split into simpler sentences: These skills were applied to the mass production of penicillin during World War II, in response to a need from the U.S. government. The antibiotic was needed to treat injured Allied soldiers; most of the penicillin that went ashore with the troops on D-Day was made by Pfizer.