Joining the Navy was a good decision for Spencer. An incident of the sinking of the Titanic in 1912, told about the heroism of the wireless operators. He signed up with the Navy to learn more about wireless telegraphy as a conseqence. He was sent to radio school and followed up his military service by going to work for Wireless Specialty Apparatus Company—which rolled into RCA—where they manufactured military and commercial radio equipment.
Spencer moved on to Raytheon in the 1920s (still around after 92 years!) and quickly became known as an expert in radio tube design. Raytheon helped to bring “radio" to mainstream America and, during World War II, their innovation worfed into a government contract where they made 80 percent of the magnetron tubes used in United States and British radar.
According to Raytheon, “… developed parts for the crucial proximity fuse in antiaircraft shells, among other equipment." They also produced something called the Sea Going microwave surface search radar that went on U.S. Navy ships. It was used to tell the ship where it was in a major battle—used in the Pacific—and it relied on a combination of sonar, radar and other weaponry to locate ships.
Spencer paid attention, met the best minds at the Massachusetts Institute of Technology (MIT), and became the expert in magnetrons, which power radar equipment. In fact, he re-engineered a more efficient way of manufacturing them and it increased the production in magnetrons from 17 units per day to 2,600 per day. He was awarded the Distinguished Public Service Award from the U.S. Navy for his contribution.
After World War II, Percy Spencer was walking through one of the labs at Raytheon and stopped in front of a magnetron, the power tube that is the engine for a radar set.