The number of guns on ships.

This is about small guns, as I have been working most with those lately. But I suppose it is the same with the larger ones.
As it is now it is possible to put 4×2 127 mmm guns on an old DD hull without that much work. Designing an a big DD with old technology in the mid-30s might be right with all the drawbacks that comes with that. But upgrading a small DD with 4 small guns, a coupple of torpedoes and some deptharges to a ship with twice that much firepower, and four or more times as heavy broadside would certainly not fit in the same hull. Not to mention the extra space needed for AA shells, the radar and the automatic cannons with all the extra crew that comes with that. As it is now I only find five types of small guns interesting.
1. Cheap guns (for example 3× 76 mm DP) as cheap AA on DD escorts for ASW duties, and pure Minelayer DDs.
2. Maximum number of cheap AA guns (for example 8× 102 mm DP) for ASW carriers and upgrading old DDs.
3. Maximum number of good AA guns with high firepower against surface targets (for example 8x and 12× 127 mm) for DDs and CVs.
4. Maximum number of costly DP guns with great AA, maximum piercing and high firepower (for example 12× 140 mm DP) for CLs and larger ships.
5. Maximum number of large guns with high firepower and piercing (for example15× 152 mm guns) for ships mostly operating outside the reach of land based airplanes.

Putting 5, 6, 10 guns or so is rarely interesting, unless one is making treaty-ships and making a good design just below the limit.

I don't know what should be done about this though. Changing from 5x 152 mm to 10x 102 mm guns as was done on HMS Coventry is easily done here. Changing to 12 would mean a change from 5x2 to 4x3, and that would require such a rebuild that it would probably not be worth it.
Some ships where planned from the beginning to be fitted with larger guns later, but it seems those where not that common. Perhaps as mentioned somewhere here it should be several subclasses of some classes. Or to all.



The other thing I hand in mind was ships with lots of float planes, mainly cruisers. After freshing up my memory on Wikipedia it seems most cruisers had 1-2, sometimes 4 planes. The Tone class of cruisers built for reconnaissance was the successor other the famous Mogami class. When the Tones was planned for 8 instead of the 3 planes on the Mogamis they also changed from five to four turrets and put all those in the stern. Much else was changed, but plain sense is enough to understand that it meant big chages to put that many planes on a cruiser with lots of 20 cm guns. All those extra hangars takes allot of space. Big guns needs to be placed in a way that doesn't change stability too much. The planes was placed all in one place, and having big guns there would not work that well.

So an extensive use of hangars should be a limiting factor for the number of main gun turrets. Perhaps the number of slots should be limited, and larger ones with bigger drawbacks be added. Or a subclass of scouting cruisers.