there's this tread about making playable units that keltos has been desperately trying to get stickied
(to no avail alas
):
http://www.subsim.com/radioroom/showthread.php?t=134575
When I first started modding it was a huge help for me. If you follow the instructions you should be able to have a working clone of a sub in no-time. You then can go edit all the basic functions/looks of this sub until it looks as you want it to.
Also, if you decide to start modding the following tool (S3D) is a must-have:
http://www.subsim.com/radioroom/showthread.php?t=119571
If you make a 3d model and textures of the sub and ask me nicely I might even import it into SH4 for you.
Takes me only about 2 hours nowadays.