Kure traded speed for a marginal armor increase

The ships had about 25 mm of deck protection, while the two Kure-built hulls received a 50 mm belt instead of the 46 mm belt fitted elsewhere. Those same hulls used the 104,000-shaft-horsepower plant and were expected to lose roughly two knots compared with their sisters. The four-millimeter increase did not appear able to stop any weapon that the thinner belt could not. It therefore offered almost no practical protection in exchange for the speed loss. The comparison shows why a measurable specification change matters only if it improves combat survivability enough to justify its costs.