Here is a picture of my Dad's vertex - looks very much like yours. He got it whilst serving in the merchant navy, he thinks around 1958. So that might help you date the watch. Interestingly, although I have no pictures of the rear at the moment, his didnt have 'vertex' on the rear of the case, just a serial number like yours (though I cant remember what it was exactly). Anyway - based on that, I would estimate the 50's as being the right sort of time line.
PS there is one subtle difference - my dad's version has the hands in gold, where as yours arent. Not sure if that affects the dating or not.