THEBERBSTERS page here on subsim, has a lot of useful info concerning SH 3, 4 & 5... would highly recommend that you go to THEBERBSTER page & click on the link there for SH3... that will be the very top one concerning installing & running SH3 and using it to get SH3 to where you can not only run it, but... be able to add in GWX 3.
Those instructions helped me to get my SH3 to work with mega mods like GWX & Living Silent Hunter 3-2015 version.
He gives a very complete lay out on how to do that.
To get to his page, just click the link below.
https://www.subsim.com/radioroom/member.php?u=303079