This is not an error but as intentional - there is no change within the same class... the Tench is a Balao ~improved~.
The change of an individual classes is subject to availability as follows:
S-/Porpoise --> Salmon/Sargo --> Tambor(Gar)/Gato --> Balao/Tench
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But there is a sensor patch, which fixes the hydrophone error at surface running.
The deck and anti-aircraft guns were again slightly more optimized towards reality.
http://workupload.com/file/qEvjGwe
It must be started a new campaign .
greetings