The North Carolina had dual purpose 5" guns, but in here they are only AA. 

http://en.wikipedia.org/wiki/USS_North_Carolina_%28BB-55%29

The Bismark, used it's secondaries with HE, yet here only AA as well, there's already a thread about that.

Even the Nelson had dual purpose weapons on it's secondaries.

My question is why is the Nagato the only t9 BB that can use HE on it's secondary weapons. With all these small boats running all over the place, zipping about, we need this extra layer of defense on the t9 battleships.