John challenged me to open up the watch, and check it out, so I did
It is an unmarked brass movement, looks like the usual #21.
In fact, check out the code at the top, it begins with 21, and I wonder if this references the movement. I don't know what the other numbers represent. Watch still seems to be running fine, which is good, I have bad luck when I open watches!
...pics of this early Timex dial/movement! It's also very interesting to see that "code" at the top of the dial. I would assume that the first two digits indeed indicates the movement. It could also be a military / MIL number? These were issued to the nurses during WWII? Thanks Alan for posting the pics and info!