Would a 15cm cannon be fine? Or perhaps a 20cm...

I like the feeling of using a 15cm more.

Wanna try adding vibration capabilities too?

Sounds good. I want to try out having it move forward and back on its own too.

Let's get some advice from Kongou-san and Shoukaku-san about the shape.

This time, realism will be vital!

But we haven't seen a real one yet, have we!