The deck guns didn't matter much, they didn't really sink stuff bigger than trawlers with them.
As for the IJN subs, it was not their doctrine to attack supply. The raison d'etre for IJN cruising subs was to whittle down the US Fleet to improve the odds for the Combined Fleet in the "Decisive Battle" they sought.
Regarding Allied ASW, you must not forget INTELLIGENCE in the calculus. We did so very well vs axis submarines in large part because we knew where they were. It's not just the ASW technology, but putting the technology in the right place, and having an ASW doctrine that continues to prosecute the attack until they have some idea of the outcome.
If the japanese could have steered their shipping away from our subs, and put what ASW units they had on top of our submarines, the Fleet boats would ahve had a MUCH rougher time for less of a tonnage bag.
tater
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