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Engineering, Vol. 63, No. 9-) A new light compact telephone switching unit developed by the Signal 'Corps, Army Service Forces, is supplanting for emergency field service the bulky switchboards hitherto used. This unit, the Adapter Plug U-4/GT, can be used for terminating a local battery telephone line, and several plugs, used with a field telephone for the operator's set, will provide a workable switchboard substitute which may be set up rapidly.
Weighing only one ounce, the plug can be transported to many spots inaccessible to a battery switchboard. It also is moistureproof which makes it invaluable for jungle or mountain operations, for beach landing in raindrenched areas, and for air-borne operations behind the enemy lines. The transparent plastic body of the plug contains fasteners for line connections, a neon lamp that responds to ringing signals, and two combination jacks and plugs for tandem connections between adapter plugs. The resistance and neon lamps are inside the plastic body which makes them virtually impervious to moisture and fungus attacks. A luminescent identification plate on which the operator may inscribe the line number is embedded in the plastic.
The plug builds up a flexible switchboard upon which the operator can make not only individual connections but also conference connections by calling individually the parties desired and connecting the adapter plugs in tandem.
The U-4/GT was developed in response to an elementary need, realized especially in the Pacific war theater, of substituting a visual signal for the bell signal. The latter could be heard from considerable distances by enemy snipers. Extension of the use of the plugs to the building of substitute emergency switchboards was a by-product. The visual signal functions when the operator attaches the field-wire pair entering his outpost to an adapter plug and connects his telephone by a short length of field wire to another adapter plug. Incoming calls flash the lamp in the first plug. R. H. O.
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