The TG-5-B seems a bit over designed for a telegraph set, but
this is the way they built things in those days. The key attached
to the front cover is a J-41-A (shown in detail below). The two
orange stamps on the cover are a Signal Corps acceptance stamp
and a Fungus Protection stamp. I assume the set was used in a
wired, or landline, field telegraph network.
(click to enlarge)
(click to enlarge)
(click to enlarge)
(click to enlarge)
Here is the circuit diagram, which is glued to the inside of the lid.
This special version of the J-37, called a J-41-A is furnished
with an extra terminal on the right side. The connecting straps
are arranged such that there is continuity between the two back
terminals on key-up, and between the two terminals on the right
on key-down.