Early in World War II, physicists in the United Kingdom invented the magnetron, a specialized microwave-generating electron tube that markedly improved the capability of radar to detect enemy aircraft. American companies were then sought by the US government to perfect and mass-produce the magnetron for ground-based, airborne, and shipborne radar systems, and, with support from the Massachusetts Institute of Technology's Radiation Laboratory (recently formed to investigate microwave radar), Raytheon received a contract to build the devices. Within a few months of being awarded the contract, Raytheon had already begun to mass manufacture magnetron tubes for use in radar sets and then complete radar systems. At war's end in 1945 the company was responsible for about 80 percent of all magnetrons manufactured. During the war Raytheon also pioneered the production of shipboard radar systems, particularly for submarine detection. Raytheon ranked 71st among United States corporations in the value of World War II military production contracts. Raytheon's research on the magnetron tube revealed the potential of microwaves to cook food. In 1945, Raytheon's Percy Spencer invented the microwave oven by discovering that the magnetron could rapidly heat food. In 1947, the company demonstrated the Radarange microwave oven for commercial use. Raytheon was also a contractor for the mass-production of the newly-invented miniature shock-resistant vacuum tubes used in proximity fuses. These tubes were difficult to manufacture and required rigorous attention to detail to avoid failure of the fuse. After World War II In 1946, the company expanded its electronics capability through acquisitions that included the Submarine Signal Company (founded in 1901), a leading manufacturer of maritime safety equipment. With its broadened capabilities, Raytheon developed the first guidance system for a missile that could intercept a flying target. In 1948 Charles Francis Adams IV was appointed to be the new President of the company and served until 1960. In 1948, Raytheon began to manufacture guided missiles. In 1950, its Lark missile became the first such weapon to destroy a target aircraft in flight. Raytheon then received military contracts to develop the air-to-air Sparrow and ground-to-air Hawk missiles, projects that received impetus from the Korean War. In later decades, it remained a major producer of missiles, such as the Patriot antimissile missile and the air-to-air Phoenix missile. Raytheon made a foray into computers, producing the RAYDAC computer for the U.S.Navy which became operational in 1953. "Unfortunately, the machine was technically obsolete by the time it