User blog comment:FlammeumDraco333/Tales From the Not so Blocky Seas/@comment-25373667-20150628023606/@comment-25373667-20150628025235

OK, well, I just heard that with some ships AP is your Primary Shell and HE is your Secondarily Shell (again, not me, telling you what the game says). I think it's mostly on battleships and battlecruisers though.