congratulations.
In some patrols U-boat commanders might not sink any ships let alone see anything for the duration of the entire patrol. and whatever radio reports they received might have been so far away that an intercept was all but impossible.
check out uboat.net and check patrol history of some of the boats there... its actually amazing the number of patrols wherein sinkings read "0"
I would say your haul of two ships is fairly historically accurate.
Be sure to save at least one fore and one aft torpedo for the voyage home.
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