Les;
I have a shot at your question, although some may disagree with
me. I think the American Gato Class subs were a well design fighting
submarine. The U.S Navy had gone to the extremes, having their fleet
of submarines go through a series of logical improvements during
WWII. They were content with the Gato Class & put it in quanitity
production. Unlike the Japanese subs, the Americans did not show
much basic technological differenence. The Japanese subs did have
a aircraft hanger in some boats & some were very huge boats the
Japanese did used during WWII. Japan showed no signs of being
influences by the American Navy, and each year during the war
produced more bigger submarines. Following the trend in their surface
warship designs towards superiority endurance & armament.
The U-boats I think were too slow & noisely, their technological
differenence was that it was base on an ex-WWI type design.
However, the U-boats were later dominated by hostile air attacks
which later failed the German Navy, because it was too slow and had
a very restricted radius of vision.

Regards Ted