Watson-Watt, Sir Robert Alexander (1892-1973), a British physicist. He developed the first successful radar system, which he demonstrated in 1935. It grew out of a radiolocator device, used to track thunderstorms, that he built shortly after World War I, while assigned to the Royal Meteorological Office's Radio Research Station. Watson-Watt was born in Brechin, Scotland. He was knighted in 1942.