The program for the regular meeting this month will be a DVD titled, “The Spies Who Lost the Battle of Britain: The Story of British Radar and How the Germans Nearly Discovered It.”

Despite the somewhat confusing title, this DVD is mostly about the Chain Home radar system Britain used to find invading German bomber aircraft at the start of WWII and thereby direct their fighter aircraft.

The Chain Home radar system used low-frequency pulsed broadcast transmitters and huge antennas in many locations. There was a vast infrastructure of (entirely manual, before any computers) plotting boards and command personnel to make the Chain Home system work–and it did work. This was before the development of microwave radar and the klystron microwave tube.

The Chain Home radar system used transmitters pulsed at 25 Hz, half the British electrical mains power system. The Germans flew missions to try to understand the purpose of the large tower antenna arrays but were thwarted by the pulse frequency, which they interpreted as noise from the mains power lines and thus failed to understand the Chain Home system, which German bombers could easily have demolished. Instead, the Germans decided to not waste resources on the big tower antennas and, many believe, effectively lost the Battle of Britain.