Teddy, if you would, please consider making the players starting rank Oberleutnant zur See. Yes, technically there were commanders who started out as a Leutnant, but, good grief, there were only 6 of them! 625 of the 1410 U-boat commanders were Oberleutnants, making it the most common rank of the war.
http://www.uboat.net/men/crew/commander.htm