The subminiature tube (developed by Raytheon) was used during W.W.II to help prevent the German "Buzz Bombs" from reaching their target in England. The technology of the day prohibited construction of the electronics needed to build a receiver that could be placed in the nose of a ground launched shell that could then be aimed toward the incoming German Missiles. Raytheon developed the "Proximity Fuze" using the "subminiature tubes", the "fuze" was in reality a sensitive metal detector that could be placed in the nose of an exploding shell that was launched towards the incoming "Buzz Bomb". When the shell came within proximity of incoming aircraft or "Buzz Bomb" it would explode. That explosion either destroyed the aircraft or "Buzz Bomb" or knocked it off course. I understand the "Proximity Fuze" was also used successfully in the pacific to knock down Japanese aircraft.

As a result of the WWII development of the Proximity fuze, a few companies made radios using even smaller versions of these tiny tubes. They were: Belmont, Private Ear, Crosley, Hoffman, Emerson, Motorola, Sears "Silvertone" and Westinghouse. Some of these sets were "hybrids" using a combination of tubes and transistors and some sets incorporated a miniature tube and 3 subminiatures. 1955 saw the last use of these neat little tubes in consumer radio products as the transistor technology was taking over the small radio design.