Let me answer before the "helium escape valve" crew get here!
A 50's watch, or any other regular watch, aren't sealed with any negative or positive pressure that is retained inside the watch. Some deep-dive watches have to be concerned with pressures but I'm sure you're ok.
However, they
do have designs to keep moisture, dust, etc. from entering, to varying degrees, and they
do have various methods of accessing the inner movement without causing damage.
I once spent some time trying to pry the back off a watch that had no back and was loaded from the front!
My point is that unless the watch is of little value or you don't care, take it to a competent watchmaker or study long and hard before attempting.
Any pictures?
