[ARC5] Mystery unit

[Kenneth G. Gordon]

In going through my stash today, I found a "Signal Corp Time Interval Unit ML-138", MFPed 
in 1944. Looks to be never used. Even has a tag wired to the mounting frame.

Not sure what, exactly, it is, although from what little I can find on the net about it, it includes 
a tone generator.

It is beautifully built inside. All brass-geared clock mechanism in there of some sort with a 
winding key mounted in the lid. There are two main-springs and two places to wind them up 
with.

Would anyone here have a clue...or even several clues?

Ken Gordon W7EKB