Might be talking about different screens, the main menu I have is this one;
Note where the arrow is pointing, I have 1.4.
I tried 1.5 last year, but I'm still chugging along on a 15 year old Dell with Windows XP, so 1.5 worked like a government employee.

As I recall though the main difference was when you chose a career, it had more options including German U boats.
Another way in XP (dunno if this applies to all them newfangled VISTA 10 fiascos or not) is to right click on the executable, choose Properties, and click Version;
That works for most programs, at least before Vista.