Actually a 90° torpedo intercept angle could cause even greater problems as the "trigger mechanism" could deform, on contact with the hull, before comencing the detonation. In this context the shots would be more "productive" if they were lightly angled (compared to a 90° angle).
But why are you that suprised? Early war german torpedoes had similar problems, too. In fact
, too similar because, IIRC, the Mk 14 was based on the exact torpedoes the U-boats used (to the more knowledgeable: please correct me if I am wrong). Didn't you get duds in SH3?
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