The cavity magnetron in World War II: was the secrecy justified?

Abstract

The cavity magnetron was invented in Birmingham University and developed by the GEC for centimetric radar in World War II. Its existence was kept secret, and its deployment was delayed, in the belief that as soon as it was used the enemy would be able to adopt the technique both in radar and in countermeasures. The H 2 S radar using the cavity magnetron was first used in January 1943, and a Stirling bomber with H 2 S crashed a few nights later near Rotterdam. The radar equipment was recovered almost intact by Telefunken engineers. The author of a German report on the equipment, Otto Hachenberg, subsequently became a colleague of the present author in radio astronomy. He died in 2001 and his report of May 1943 was discovered among his papers. It reveals that the principle of the cavity magnetron was already well known in Germany, based on work published in Leningrad in 1936. The most serious effect of the delay in deployment of the magnetron in centimetric radar was in the anti–U–boat campaign, in which the new centimetric radar became the main contributor to the successful end of the Battle of the Atlantic.