In the aftermath of the Tizard Mission, American forces prepared for the contingency of operating in Britain. This included learning to operate under the British Chain Home air defense radar that proved crucial for Britain’s security during the Battle of Britain and the Blitz. During the initial operational employment of the Chain Home, the limited radar coverage and organizational resources were directed at locating approaching enemy formations, rather than tracking friendly aircraft over British soil. Locating the interceptors to direct them to enemy formations required an interim system of location consisting of established radio direction finding (RDF) networks.
The “pipsqueak” identification unit contactors like this one were the solution before the advent of dedicated IFF transponders. They were essentially timers for communications radios that broadcast a fourteen second carrier wave every minute, which allowed the RDF stations to determine a fix (but also prevented the pilot transmitting during a period indicated by the arc on the dial). The BC-608 “Pipsqueak” was an American variant of a British unit developed in 1939 that entered production in January 1942. As the Chain Home system grew in capability and coverage, the need for the contactor disappeared and true IFF (Identification Friend or Foe) transponders took their place. Production was only about 500 units.