Before starting your first patrol
don't purchase any equipment upgrades (it's probably not a good idea to buy new crewmen or officers either). There is a long standing & unsolved bug in the game that may prevent you from getting credit for any ships that you sink during that 1st patrol. One workaround is to wait until you've completed your 1st patrol then do any upgrading just before you leave for your 2nd one. Or you can perform a "shakedown" cruise: leave the harbour as you would in a normal patrol, do a few maneuvers (diving to periscope depth, etc.) & return to base. You won't get credit for anything of course but you won't lose any renown either & you can now upgrade your boat and get credit for any tonnage that you sink since you're now on your 2nd patrol.
Welcome aboard & good hunting...
