Had a look at the museum's website but couldn't find the Underwood being discussed. Still want to know how it was determined to be a radio mill versus a telegram model since all the characteristics you listed are true of telegram models.

Uwe wrote:

mre12ax7 wrote:

I have not the slightest clue to what this thing does.

Wow, if I was anywhere near Columbus I'd be buying that Underwood 3 immediately. In fact, it's the most exciting machine I've ever seen in a CL ad. Too bad there aren't better pictures of it, but my guess is that it has a motor-driven platen controlled by the lever on the left side of the keyboard. Why? Well, most likely it was used as a telegram machine that pulled paper off of a large roll and by having a platen that could be advanced without a typist's hands having to leave the keyboard must have sped up things. 

I'd love to buy it; hmmm, I wonder if the seller would ship it? 

You know, a thing like that reminds me of what I saw on a 1932 Burroughs electric.  Well, the only thing electric about that typewriter was the return.  My guess was that when you pressed the return, a motor turned on, grabbed the drawstring somewhow, and pulled the carriage to the right of the machine until it hit a stop/trip mechanism that shut the motor off.  The motor was probably an intermittent duty motor--like one you'd find in an old adding machine, and probably in this present typewriter.  It seems, without having seen a picture, that what this typewriter has is a power vertical injector.  I'd never heard of it before, but there's a lot of things in the realm of office equipment that is quite unusual--and fascinating!!