I know this has been asked before (as I did a search here), and there were plenty of responses:
How do you mod the config files so that you can obtain a type XXI in 1939?
Now the thread that I found (and it took FOREVER TO FIND THE THING!!) the person posting showed several long posts of what it was they had changed, but were having problems in game. There were several comments back and forth, but no answers really, to where the person had to do a whole reinstall!
Of course, many of us simply use SH3 and GWX as it is. But there comes a time when curiosity and the wanting to do something becomes powerful enough to want to try something.
So I'll ask the question again:
Is there a tutorial or posting that shows how to modify your configuration files so that you can make things like the Type XXI u-boat and other equipment available earlier? One that works?