Armour improvements

[MikeBrough]

A statement in the on-going Bismarck vs Rodney thread pointed me towards some reading. The post in question suggested that Rodney's mid-1920s armour was significantly inferior to that of the late-1930s Bismarck.

A statement in Brown's Nelson to Vanguard confirmed this saying that the cemented armour used on the KGVs was about 25% more resistant to penetration. What was really interesting though was the side note saying that similar changes were made in Germany about 1930 but that the USA weren't aware of these changes until 1939 by which time it was too late for any of the USN battleships.

Is this correct? If so, was USN armour basically the equivalent of Rodney's or was the USA making independent, parallel advances in their armour quality? Again, if the latter, where on the curve did USN armour fit in the progression from 1920s - 1930s RN armour?

[alecsandros]

It's probably impossible to quantify exactly the improvements done in armor quality between the wars.

There are some tests that can help, but not that much.

Cross-country comparisons are extremely difficult to do, and should be treated with caution and within a generous interval.

I don't think US class A armor was 25% less resistant to perforation than British post-1930s CA, and my bet would be that , on average, the plates would be 5-10% less resistant than their British counterparts at the most.

What should be noted though is that the producing of heavy plates was difficult, and every country had various technologies in use. Corresponding to those technologies were different "maximum thicknesses" of heavy plate while retaining full resistance to perforation.
Krupp for instance found that their plates could be of maximum 320mm thickness, and any milimeter above that thickness would not retain same resistance.
For instance, a 330mm Kurpp plate would be similar to a 325mm high-quality plate.

US manufacturers discovered a 305mm (12") limit of their producing quality.

All the best,

[alecsandros]

A small addition:
The US Navy's need to employ very thick plates for their turret faces and barbettes made them opt for class B (homogenous) armor plate, because of the reason mentioned above. Thus, a 450mm thick class A armor would be very difficult to produce, and would retain no more than 360-380mm of the thickness of a good quality plate.

[Dave Saxton]

Krupp for instance found that their plates could be of maximum 320mm thickness, and any milimeter above that thickness would not retain same resistance.

This doesn't apply just to the Krupp plates. This is the thickness of diminishing returns for all face hardened armour. This fact makes using 17"+ turret face plates seem kind of silly. The effective thickness at a high quality standard will be only be about 15" anyway.

I don't think US class A armor was 25% less resistant to perforation than British post-1930s CA,

I think it was, and so did BurOrd. It had to be pretty bad to go ahead and use Class -B instead. The Class-B plates were not up standard either- being about 80% in terms of penetration resistance. BuOrd knew this, but still went ahead and used them in place of Class-A.

There's book about BurOrd by the BurOrd during and before WWII. Get the 1st edition, not the cleaned "Benghazi Cover UP" edition.

An interesting fact about USN armour development was that no R&D happened between 1925 and 1935. In 1935 the whole department was run by two jr officers. They had to play catch up. Private firms like Carnegie and Midvale went to Krupp for advice during the late 30's. (I have read the engineering journals reporting on this.) But they didn't have the advanced manafacturing facilitiies needed to replicate the Krupp metalurgy.

The Germans in violation of Versailles had been forging ahead with armour and shell R&D the whole time.

[phil gollin]

.

Just to agree that strict comparisons between nations was difficult as testing was severely limited and armour penetration was a statistical matter NOT an absolute. Testing of armour and projectiles was INTER-DEPENDANT and NEITHER was an absolute. The limits given were arrived at by doing multiple tests and then a decision was made at where to call the limit (different nations would make their own decisions). Different projectiles (both individual and batches) and different armour batches would have slightly different properties.

Having said that there are contradictory comments in the Ships Covers files re. British armour. It is agreed that Hood's armour is better than previous, BUT that the Nelsons had a definately improved armour. What is contradictory is as to whether the KGVs were better than the Nelsons - there are statements to support both. I would go for the KGVs being better because there is also a statement re. Warspite's armour added in her modernisation which SEEMS to say the mid-30s armour was appreciably better than the 20s.

HOWEVER - nothing definite