Is it possible to rework these shells to be more historically accurate. The IJN were obsessed with delayed action fuses on these shells to improve near miss underwater damage, so they created a lot more flooding and below waterline damage than other nations shells of this size. It also made them more effective vs superstructure. The mechanism was simple that the fuse action delayed so as not to explode on contact with water and softer materials allowing some travel underwater before exploding. However this made them less effective vs armor where impact would more likely explode the filler inconsistently before the detonator. It’s hard to find any data other than the fuse diagrams that show the variable fusing that would allow such and anecdotal evidence of the obsession with such mechanism until the 1930s. Maybe Gaijin has more details on this. At present the HE shells are fairly poor in contrast to other nations which did not seem to be the case in historical recorded action such as the Battle of Bandung Strait, specifically the action with HNLMS Tromp.
Japanese 127mm shells are working historically in the game. IJN never developed delayed fuze allowing underwater travelling for their 127mm guns.