The Japanese realised, while only two units of the Tenryu class were under construction, that that size of cruiser would not be of much use in the wide open spaces of the Pacific. Bigger ships with better range, speed and size would be required.
1938 and the Kuma class are coming up 20 years old. The low angle 5.5" were of no use for anti-aircraft use and to make the ships more useful, some form of conversion to an anti-aircraft cruiser would extend their first line lives.
Above: real life IJN Kitakami as a torpedo cruiser with 40x24" torpedo tubes - 20 per side. Armament only 2x5" AA plus lots of 25mm.
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The single 5.5" mounting weighed in at about 20 tons each. The twin 5" DP turret was about 38 tons per mounting. The single 5" DP turret weighed in at 22 tons. During the same refit the twin 21" torpedoes were replaced with 24" mounts. To balance the additions, the aircraft and handling facilities were removed. The three funnels were trunked into one. Two twins and three singles made up the 5" DP armament.
