Get the Flotilla Mod. Lets you start with the 2nd in wilhemshaven(sp) 3 Sept 1939. I think the latest is version 1.44. Available at beery's site and others. There are a couple of very cool new features.
IXB is an option immediately but, unless you edit renown, 4 or 5 patrols away. Assuming you had 1500 from the academy as initial stake. Cost is 9000 and drops to 7500 renown about jan '40 IIRC.
GL&GH
PS heres some linkie action
http://www.beerymod.com/sh3.htm