I think the choice of boats at any given time depends on what flotilla you're in. I don't know how that pans out in GWX by itself, I've always started careers with SH3 Commander.
Which, if you're going to play SH3, you should get anyway.
When you start a new career from Commander you can choose your start month/year, choose your flotilla (which will determine your home base), and then see which boats are available in that flotilla at that time. Find one that will let you start in a Type II and you're good to go.
I use the "historical availability" option so I assume I'm limited to whichever boats each flotilla actually had on a particular date - but if you don't use that, it's possible that you can pick any flotilla/base and then have your pick of u-boat types to choose from.
Sticky thread on Commander here:
http://www.subsim.com/radioroom/showthread.php?t=147237
For a lot of folks it's a must have, it will add so many options to managing your crew and career - can't imagine playing without it at this point!