Informationen zur

Circa: W.W.I
Maker: Western Electric Co. Inc.
Used by: Signal Corps U.S. Army

The key was part of a SCR-71 Ground-Return Telegraph Trench radio Set (BC-16), basically a copy of the French TPS (La Telegrafie Par Le Sol = Earth Telegraphy).
S.C.R. stands for Set Complete Radio or later Signal Corps Radio* and refers to the complete radio system, whilst B.C. means Basic Component and refers to a system component of the radio system. (Both SCR and BC are U.S. Army Signal Corps designations).

The key has a 5-5/32 x 3-3/8" wooden base.
It is a telegraph key with an adjustable, folding lever (or rather: a lever that swings to the left side).
The tension spring extends from the lever through the wood base. Larry Nutting K7KSW says that the Americans copied the J-3 from the British.
The J-3 was used in the US Army set SCR-71 (BC-16). The British had the same type of set, with keys they made.

J-3 variations:
There are some differences between various J3's however. Found those limited to the colour or finish of the
wood base - some are painted, some are stained and varnished and the binding posts. Some are simply screw types,
some conventional type with knurled hardware and some with very large Fahnstock clips.
When the lid of the transmitter box is closed, part of the key lever and knob stick out and the key can be used.
However, to protect the key during carrying and shipping, the lever can be folded and fits inside the box.
The key is identical to the French folding key, integrated in the type 4 spark transmitter made by Radiguet & Massiot of Paris France.
There was also a J3A key, which was a later version of the J3.