If I remember rightly, this is a bug connected with upgrading your u-boat before commencing your first patrol. It can result in no renown being awarded even though you sunk allied ships. If you made a save prior to docking at base then you could reload that and dock again. This usually cures the problem.
I must admit that I have had this bug affect me even though I hadn't made any changes to my boat, but I believe the general consensus is as above.
Nemo
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"I'm afraid there is no disguising the fact that King's obsession with the Pacific and the Battle of Washington cost us dear in the Battle of the Atlantic".
Sir John Slessor GCB, DSO, MC, DL
AOC-in-C Coastal Command RAF
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