While discovered by Alexander Fleming in 1928, penicillin was not mass-produced until WWII. Spurred by the need to treat infected wounds and diseases like pneumonia, Allied scientists perfected deep-tank fermentation. By D-Day, 2.3 million doses were ready for Allied troops. It is estimated that penicillin reduced the death rate from bacterial pneumonia in soldiers from 18% in WWI to less than 1% in WWII, saving hundreds of thousands of lives and earning it the nickname the 'Miracle Drug.'