Boxes, boxes, everywhere...

The explosion of avionics on WWII aircraft quickly made control boxes almost unmanageable from a human factors standpoint. It was roughly the equivalent of the 1930's household that had one ceiling light fixture, from which emanated multiple extension cords hanging all over the walls and floor. Add to it the lack of consistency on where the boxes were mounted from aircraft to aircraft, and you had a real mess on your hands. Sometime in 1944, someone had the bright idea of emulating the 19" rack mounting system long used in industry to solve the same problem. The new width standard was 6" to accommodate the smaller control constellation required for each avionics device, but the idea was the same - stack them up and hide all the connecting cables from view and possible contact. The particular control heads shown below were most closely associated with the ARC-5, though they were later used for other sets - a tribute to the effectiveness of the modular concept. About 1948 the width was changed to the 5 3/4" standard still used today, with backlit plexiglass overlays and Dzus fasteners substituted for the panel screws for speed in removal and replacement. Many of the older units were converted to this later format by chopping off a little on the sides and installing the Dzus fasteners. As a result, these early rack panels have become quite scarce.

Three of the 6" rack series boxes

The three control heads above are the C-125 for an ARC-5 receiver, a C-126 (functionally identical to the C-38A/ARC-5, less the ARR-2 control portion) and a C-127 master power/volume control. The C-127 has been modified as mentioned above, and will get returned to its original configuration before mounting. The C-137 was a minor variation of the C-126, so is not shown here.
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