Cavity Magnetron
The cavity magnetron was a turning point for the use of radar during the war as it allowed for radars to be placed on night-fighter aircraft, anti-submarine aircraft and escort ships. The first magnetron was developed by H. Gerdien in 1910, the split-anode magnetron was developed by Albert Hull in 1920. Experiments with different magnetron devices continued and in 1935 Hans Erich Hollman applied for a patent for a multiple-cavity magnetron. All of this led up to the development of an improved cavity magnetron tube by John Randall and Harry Boot in 1940.
Their device was able to produce high powered pulses which made centimeter-band radar practical. The shorter wavelength radar allowed for the detection of smaller objects while using smaller antennas. The cavity magnetron was compact enough that the size of radar sets was reduced and therefore easier to put into use. This allowed pilots to get maps of the ground in order to see their targets even in the middle of the night. It was even able to catch the periscope of German U-Boats so that bombers could target subs just below the surface of the water.
It was far from perfect due to the magnetron’s instability in its transmitter frequency and the wide frequency spectrum of the transmitter pulse which requires the receiver to have a wide bandwidth as well. Today the cavity magnetron has largely been replaced with semiconductor microwave oscillators. Even if the cavity magnetron is not used in radar anymore it is still very effective for another purpose for which is it more widely used. It is the heat source used to cook food in a microwave oven thereby making daily life easier for many people around the world.