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The anti-warship role they settled on made sense in the perceived strategy - lure the US fleet out, damage and reduce it by air and submarine attacks, then sink it with battleships. Of course, they didn't seem to bother with why the USN should so obligingly fall into this trap, but the earlier US war plans did have them doing this - they weren't changed into something more sensible till quite close to the war.
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Arguablly the IJN submarines did more damage to the USN aircraft carriers in 1942, than the IJN carriers. Most folks are unaware or forget the Saratoga was twice taken out of action for months by two submarine attacks. Another was sunk outright, and the savagable Yorktown sunk by submarines.
The Pacific isn't as big as all that when you consider it ratioinally. You're making the same mistake Nimitz (or Withers & English) made: you're looking to scatter boats all over the ocean. Look at the trade routes. Look at the ports. There are a small number of "ideal" places, & there's everywhere else.
Still the IJN did not have enough submarines to operate this either. With the number of submarines they can have on interdiction stations & if they have a average number of hit comparable to the Germans at their peak, the potiential tonnage of cargo ships sunk or damaged is still 'small'.
Interdicting Hawaii is the same, & an especially vulnerable target...![]()
Nearly 20 IJN submarines operated near Hawaii in December 41 - January 42 with the express purpose of interdicting ships coming and going. they managed to get one significant hit, on the Saratoga. concentrating closer in, and altering doctrine for targets could have nailed 3-4 cargo ships, but...
The problem with concentration of raiders is the defender can concentrate as well. The Germans ran into this problem when Allied ASW resolved its problems through 1942. In 1940 a effort to concentrate on the near approaches to the British ports of the UK ran up unacceptable losses (re: Huges & Costello 'Battle of the Atlantic') They forced the relocation of the submarine Patrols to a more dispersed pattern furhter out in the Altantic. A similar thing ended the massacre in US coastal waters in 1942. byt the autum of 1942 neither the east coast or Carribean were safe for the Germans. Again they had to relocate into the mid Atlantic.