The earlier interphone systems and jack boxes

BC-213 jack box (at far left), with FL-5 range filter, its associated BC-345 selector box, and a BC-335 jack box at upper right
From a simpler era of small planes and smaller crews, the BC-213 included a selector position for radio and interphone system combined, a position that would be hard to sort out in combat with a 10 man crew. The BC-213 and the BC-212-* amplifier most often paired with it were components of the RC-15 (Radio Component) interphone system introduced in the early 1930s, though a subsequent RC-27 release in the mid to late 1930s included components that were produced well into the war to keep older aircraft logistically supplied.

BC-212-D interphone amplifier
An "add-on" capability to ease the use of the radio range navigation system was RC-32, composed of the FL-5 and BC-345 selector box. It reduced aural fatigue caused by radio noise while listening for the guidance code tones generated by the radio range system. It was designed for the HS-23 headset, but of course could also be used with the later low impedance HS-33 by using the MC-385 transformer.

BC-335 jack box
For some reason, certain of these jack boxes are less common than others. By the war's end, many of the peripheral items that were common in 1941 had been replaced by later equipment, and the 1930's components remained largely only in trainers and the like. The BC-335 above is one of those rarer items.

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