If Japan retained the 40 mm pom-pom

What if Japan had retained and developed the 40 mm pom-pom instead of adopting the 25 mm Type 96?

Its reliable high-volume fire could have strengthened close-range defense and made American air attacks more costly.

The counterfactual replaces Japan's 25 mm Type 96 battery with continued development and stockpiling of the 40 mm pom-pom. That weapon offered reliability and a large volume of fire. Bofors-type systems had longer interception range, but a dense close-range barrage remained valuable and could tolerate somewhat less refined ammunition. A well-supported pom-pom fleet would make American air attacks harder and could reduce Japanese losses while increasing attacking losses.