To take these observations in order...
They were in a cycle where you CAN armor against the weapons of the day. But said armor is heavy.
The armor rough rule of thumb in that era was a WAG in that plate thickness of the compound/composite layered thin hard steel faced thick wrought or soft iron/steel backer equals the shell cross section diameter plus 10%. Remember the shells are still mostly Paixhan shell based type bombs with assorted French derived or British nose fuses. The shell bodies in the 1870s to 1890s were CAST IRON with at best guncotton filler.
Nasty and DANGEROUS to the senders as well as to the receivers. The armor worked because the shells were no good. We, moderns, have examples of some navies, (Chinese and Spanish) actually adjudging that "sawdust filled slugs" were better than the shoddy explosive filled ammunition their governments bought. Were they right? The Japanese made their own cast iron and later mild steel shells with Shimose, explode on second shock impact filler. It was extremely dangerous shock sensitive stuff to fire, but it worked for them. The Americans accepted a high dud count instead and used STEEL shells and British style fuses and stabilized fill that needed a detonator. Lots of clangers.
So guns grow to defeat the armor. Again they are heavy.
To deliver massive cargo shells with sufficient filler to explode against the plate, not necessarily punch through it. There is some question (depending on which navy and who made the plate.) whether the armor or the shell would shatter under the impact. Cross your fingers and pray?
Given the lack of alternative solutions it is a cycle that lends itself to gigantism. No QF guns so you can't burn them out. Not torps so you can go under. All these big weights up high encourage lowering the freeboard with the bonus of reducing the area needing to be armoured. Even Victoria's single turret is a reaction to the increasing masses.
There comes a time when one has to play the %s. The Italians figured that being hit by chaser guns was a low % so they deliberately thinned the (Harvey) armor in the Giuseppe Garribaldis to just handle 15 cm and below QFNR shots by using a new idea called shatter-gap. Smart guys. When the Cristobol Colon was shot up, how did it work out? NTG. It turns out 20.3 cm STEEL shell, the few (4) that punched through and delayed just enough to explode INSIDE the hull was enough. What a mess. The 33 cm hits did not help either.
Anyway, the US 15.2 cm steel shells did bounce off the Cruesot steel plate on the IMTs which shows that bad fuses and French steel mean you are somewhat safe until the 20.3 cm *(8 inch) stuff hits. Then it is time to beach and abandon, boys. The British laughed at the Brooklyn and the Indianas, you know?
The Italia class arguably showed the ultimate evolution of this by giving up on belt armor altogether in favour of floating, and could have worked given the weapons that existed when it was designed. But then they invented QF weapons...
And of course the Ansaldo compound iron plate scheme with the thin steel facer was BRITTLE. Too much sulfur in the iron. Hence imported Harvey plate from the UK and US when the (Giuseppe Garibaldi) GGs were a thing.
QF weapons were a genuine paradigm shift and fucked up all kinds of designs. See the HMS Polyphemus McPherson mentioned.
Yeah. The admirals who proposed these modernized Davids were just one gun armor cycle behind the curve. Refer to the Giuseppe Garibaldi comments above.
To be more accurate QF weapons when combined with reliablish shell of both the AP and especially the HE variety were the big game changers
Shrug. 50% dud rate in those days was "outstanding".
BTW... The thought has occurred to me that a shootout between Brooklyn and Cristobol Colon would have shown interesting lessons to be learned.
The CC had a top hat scheme about 15 cm on the belt and 3.8 cm on the flat deck. The belt thinned to the ends to about 8 cm. Conn was 15 cm and gunhouses' mantlet faces same with other faces and guns shields 5 cm.
The Brooklyn had a derby scheme with a 7.6 cm belt and behind that a turtle-deck armor topper over machinery at 15 cm thick on the slope presents and 7.6 cm at the flat thinning to 5 cm at the ends just beyond the barbettes. Gunhouses were 14 cm mantlet and sides and 10 cm roofs. Hoists were 7.5 cm. The barbettes were 20 cm to 10 cm depending on present face. The Conn was 21 cm uniform.
Float reserve was an astounding 50%. No wonder Spanish shells did almost nothing. She was better protected than an Immortalite.
Anyway, IF the CC had been armed as planned (from Wiki)
vs Brooklyn (also from Wiki)
; it would have been an interesting to see the results.
I suspect the outcome would have been much the same, but would have impelled the Americans even more away from a Marceau type layout and toward the all big gun double enders they will build instead of the European wing turret abortions that grow out of the last PDNs they will build (See illuustrations), I have seen as RTL evolved in the South Carolinas. Maybe a full decade earlier. How about them apples?
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