[Boatanchors] Navy Mill - Underwood - Mystery Key Set Up

[Mr Bill Mellema via Boatanchors]

Guys,
The USS Wisconsin Radio Club purchased an Underwood "Mill"  for our WWII position we are setting up on the ship. It is all upper case as you would expect but the top right key which should be a 0 with a slash is a just a vertical line. In order to type a 0 with a slash you would have to back space for the zero...it makes no sense to me. I feel it is a communications mill because who else would use an all CAPS typewriter? 

I would appreciate any comments on this. It's a great old mill that will have a permanent home of the Big Wiskey.
73's
Bill N3WM