The "cavity" magnetron was a radical improvement introduced by John Randall and Harry Boot at the University of Birmingham, England in 1940. Their first working example produced hundreds of watts at 10 cm wavelength, an unprecedented achievement. Within weeks, engineers at GEC had improved this to well over a kilowatt, and within months, 25 kilowatts, over 100 by 1941 and pushing towards a megawatt by 1943. The high power pulses were generated from a device the size of a small book and broadcast from an antenna only centimeters long, reducing the size of practical radar systems by orders of magnitude. New radars appeared for night-fighters, anti-submarine aircraft and even the smallest escort ships, and from that point on the Allies of World War II held a lead in radar that their counterparts in Germany and Japan were never able to close. By the end of the war, practically every Allied radar was based on a magnetron.