Japan trades later Yamatos for convoy escorts

What if Japan used the second pair of Yamatos to build 48 ASW escorts and six modified Ryujo-type small carriers, all ready before 7 December 1941?

Japan would be better prepared to protect trade and make American submarine attacks harder, although six convoy groups would remain limited coverage.

Forty-eight antisubmarine escorts and six small carriers could form roughly six convoy escort groups before Japan entered the war. Their effectiveness depends on fitting sonar, radar and other systems that Japan had developed but did not employ widely. Those groups would make American submarine operations more difficult. American concern that the radio traffic needed to coordinate group attacks would reveal submarine positions helps explain the value of stronger Japanese escorts in this assessment. Six groups would still be a small force for the convoy task, so the improvement would have limits.