Exactly - that article was very interesting!
I can phrase my question differently. Instead of asking if armour was useless, I will ask which cruiser's armour proved its value and saved the ship? E.g. USS San Francisco at Guadalcanal - did her armour really defeat 5", 5.5" and 6" shells? Or was she hit mainly at the not armoured parts?
According to the damage report:
http://www.researcheratlarge.com/Ships/CA38/GuadalcanalDamageRpt.htmlMost damage was caused by 6" guns! She was hit by 2 14", 10 8", 15 6", 5 5.5" and 13 5". Many large caliber hits were by bombardment ammunition - not AP or HE. She was hit only 2 (!!) times on the belt: one 6" was defeated, one 8" not. Still several compartments were flooded because of other hits. The only evidence for useful armour was the conning tower, which survived an 8" hit (not clear what kind of ammunition) - but remember that most of the leading personal was killed on the not armoured parts of the bridge. And the mentioned 8" hit on the conning tower strongly contributed to the damage on the bridge. And, very interesting, that the barbette armour defeated the 14" shells (because they were not AP)!
There were some long range gun battles in the European theatre and early in the war - e.g.
Exeter's engines were destroyed by 8" fire and part of
Admiral Hipper's boilers by 6" fire.
Splitter armour and subdivision for sure proved its worth. But I guess that the Atlanta class was not badly designed in that aspects.