There is currently a problem that I have no solution for with "Conning Towers / Turms" upgrades for the Type VIIC / IXB and /IXC subs. The system at random will corrupt the users "saved" game files with US equipment vice German and make the campaign unplayable.
You can read more about this here
http://www.subsim.com/radioroom/show...postcount=1693
http://www.subsim.com/radioroom/show...postcount=1700
as stated in the above post, the only sure fire fix is to disable the Turm upgrades and hard wire the conning tower on of the mid-war ones
At this time I will not post my "Slede-hammer" fix unless I hear more users reporting the problem.
Be advised that I have created this problem more once over the last few days and if it happens to me, it will happen to you. Also be advised that if it happens, your career is "toast"