The influenza pandemic of 1918 and 1919 had a major effect on World War I, and it motivated the U.S. military to develop the first flu vaccine. Scientists began to isolate flu viruses in the 1930s, and in the 1940s, the U.S. Army helped sponsor the development of a vaccine against them.

The U.S. approved the first flu vaccine for military use in 1945 and for civilian use in 1946. One of the lead researchers on the project was Jonas Salk, the U.S. scientist who would later develop the polio vaccine.

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The world’s first antibiotic, which has prevented millions of deaths from infection and disease, was the accidental byproduct of a messy workspace.

Alexander Fleming, a bacteriologist in London, returned from a vacation in 1928 to discover that one of the petri dishes in his lab had mold growing on it— the result of unintended contamination. On closer inspection, he saw that the area around the mold was free of bacteria. Fleming named this bacteria-killing mold juice penicillin after the species of fungus, Penicillium notatum, and published a paper about his discovery in 1929. However, he wasn’t sure if it had any practical use, as it was difficult to purify and stabilize.

A decade later, chemists at Oxford University read Fleming’s paper and took up the project of turning penicillin into viable medicine. It was first tested on a patient in 1940, and widespread use began in 1942. Today, penicillin is the most commonly-used antibiotic in the world.

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Frank Whittle, an English engineer with the Royal Air Force, filed the first patent for the jet engine in 1930. But the first country to fly a jet engine plane was Germany, which performed a flight test of its model on August 27, 1939, just a few days before the country invaded Poland.

“Both Germany and Japan had been really getting ready for World War II for about a decade,” says Rob Wallace, the STEM education specialist at The National WWII Museum in New Orleans.

With the onset of the war, the British government developed planes based on Whittle’s designs. The first Allied plane to use jet propulsion took flight on May 15, 1941. Jet planes could go faster than propeller planes, yet also required a lot more fuel and were more difficult to handle. Though they didn’t have an impact on the war (they were still early in their development), jet engines would later transform both military and civilian transportation.

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During World War II, a U.S. surgeon named Charles Drew standardized the production of blood plasma for medical use.

“They developed this whole system where they sent two sterile jars, one with water in it and one with freeze-dried blood plasma and they’d mix them together,” Wallace says.

Unlike whole blood, plasma can be given to anyone regardless of a person’s blood type, making it easier to administer on the battlefield.

In the 1940s, the word “computers” referred to people (mostly women) who performed complex calculations by hand. During World War II, the United States began to develop new machines to do calculations for ballistics trajectories, and those who had been doing computations by hand took jobs programming these machines.

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The programmers who worked on the University of Pennsylvania’s ENIAC machine included Jean Jennings Bartik, who went on to lead the development of computer storage and memory, and Frances Elizabeth “Betty” Holberton, who went on to create the first software application. Lieutenant Grace Hopper (later a U.S. Navy rear admiral) also programmed the Mark I machine at Harvard University during the war, and went on to develop the first computer programming language.

In Britain, Alan Turing invented an electro-mechanical machine called the Bombe that helped break the German Enigma cipher. While not technically what we’d now call a “computer,” the Bombe was a forerunner to the Colossus machines, a series of British electronic computers. During the war, programmers like Dorothy Du Boisson and Elsie Booker used the Colossus machines to break messages encrypted with the German Lorenz cipher.

The first practical radar system was produced in 1935 by British physicist Sir Robert Watson-Watt, and by 1939 England had built a network of radar stations along its south and east coasts. MIT’s Radiation Laboratory, or “Rad Lab,” played a huge role in advancing radar technology in the 1940s. However, the lab’s original goal was to use electromagnetic radiation as a weapon, not a form of detection.

“Their first idea that they had was that if we could send a beam of electromagnetic energy at a plane, maybe we could kill the pilot by cooking them or something,” Wallace says. “The cooking thing wasn’t working, but they were getting bounce-back that they could receive and they had the idea that they could use electromagnetic radiation just like they used sound radiation in sonar. So they started working on radar.”

Radar helped the Allied forces detect enemy ships and planes. Later, it proved to have many non-military uses, including guiding civilian crafts and detecting major weather events like hurricanes.