Refitting of ships - Armor?

[Garyt]

When a battleship would be re-fitted, for instance as the Kongo class was numerous times, or when the US battleship damaged at Pearl were brought back into action, was the armor also replaced? For instance, if you have a ship from 1918 vintage that is refitted in 1942, does it have armor of the earlier time period or does it get the newer (and more effective) version of armor?

This can of course be different from ship to ship, but is anyone aware of armor being replaced on these refittings?

How about when armor was added? IIRC, deck armor was often increased on WW1 era ships in the inter-war period.

[aurora]

HMS HOOD
The addition of extra armour in the final design represented a significant improvement; without it, the immunity against German 380mm shells would actually have been negative. Despite the addition of some 3,450 tons of additional armor and protective plating, however, Hood was still considered vulnerable to long range fire. #
Although several schemes were put forward to update her over the years, none were ever carried out. Although as late as 1940, Jane's Fighting Ships was stating that ". . . the general scheme of protection is most comprehensive," in Admiralty circles her actual protection was always considered marginal. In 1920, trials with built up targets representing Hood were conducted and showed that her magazines could be reached by a 15-in shell penetrating the 7-in [178mm] belt.

In a number of almost incredibly prophetic diagrams, the Admiralty sketched the path of the shells and showed how the addition of 3-in [76mm] of additional deck armor could have prevented potential disaster.

[aurora]

HMS QUEEN ELIZABETH

She was rebuilt twice between the world wars; in 1926–1927 bulges were added, the funnels were trunked, four 4 inch guns were added, and a new foretop was installed. In her 1937–1941 rebuild she was fitted with a tower bridge in place of her old bridge; her 6 inch (152 mm) guns were removed and in their place received 20 4.5 in (114 mm) guns and several smaller anti-aircraft guns; horizontal armour was added; engines and boilers were replaced; and the elevation of her main battery was increased to 30 degrees.

Deck armour was increased to 5 inches over the magazines, 2.5 inches over the machinery, while the new 4.5" guns had between 1 and 2 inches of armour. She also received facilities for aircraft with a launching catapult amidships. New fire control equipment was installed, including the HACS MkIV AA fire control system and the Admiralty Fire Control Table Mk VII for surface fire control of the main armament.

This reconstruction was completed in January 1941, when Britain had been at war for over a year.[/b

HMS WARSPITE
1,100 tons of armour were added, improving coverage forward of A turret and the boiler rooms, as well as an increase to 5 inches over the magazines and 3.5 inches over the machinery.

]

[Garyt]

So from the info you have there, Aurora, it looks as though if armor was added, it was indeed of the newer type.

Any info on armor being replaced as opposed to just added on?

And I wonder what 3" of armor over 3" would do. If the older armor was per Okun's calculations a .90 quality, and the newer was a 1.0 quality, would you have in essence 6 inches of .95 quality?

Or if the newer armor is the top layer and face hardened as well, would the effectiveness of the armor be better represented by the quality of the top layer, for instance 6 inches of 1.0 armor using the above as an example?

[aurora]

Quote Garyt
"And I wonder what 3" of armor over 3" would do. If the older armor was per Okun's calculations a .90 quality, and the newer was a 1.0 quality, would you have in essence 6 inches of .95 quality?

I afraid I must answer "I don't know" whether it was per Okun's calculations and mathematically 0.95 quality is fair

"Or if the newer armor is the top layer and face hardened as well, would the effectiveness of the armor be better represented by the quality of the top layer, for instance 6 inches of 1.0 armor using the above as an example"

Again -mathematically -Yes

[Dave Saxton]

The added armour was simply added over top of the existing armour in most cases. The British found that two pieces of armour in direct contact provided less effective thickness than if the two plates were spaced apart from each other.

How can the effective thickness be calculated in such a case. Krupp developed a formula. In the absence of such factors as de-capping, and yaw, it was (square root) of P1^ +P2^...

Thus 3-inches of old armour plus 3 inches of new armour = 4.13" new armour

The same applies to armour plates laid over top of a structural deck. It is not the deck plus the plate. For example, 120 mm plate laid over a 32mm thick deck structure of the same material, yield an effective thickness of 124mm.

The old battleships were up against it. Adding deck plates added the full weight of the plates but it yielded only a marginal improvement in ballistic protection. For example, the deck protection of West Virginia was 1.5" thick deck structure made only of only mild steel !, with 1.5" of homogenous Special Treatment Steel plate laid over top. This was very weak deck armour, weaker than Hood's. Adding a couple more inches over that meant that it had the weight of 5 inches of steel but provided only about 3" worth of protection.

[Garyt]

I was wondering about that (The inefficiency of layered armor) as well Dave. I was wondering if there was perhaps a way when the additional armor was added that it could have made it more effective than 2 separate layers, such as perhaps welding the layers together.

[Dave Saxton]

I was wondering about that (The inefficiency of layered armor) as well Dave. I was wondering if there was perhaps a way when the additional armor was added that it could have made it more effective than 2 separate layers, such as perhaps welding the layers together.

The better way would be to use a proper spaced array arrangement. But obtaining the proper amount of spacing and the thickness ratios may not be practical.

Better yet would be the complete removal of the old main armoured deck and structure and replacing it with a single plate of new material comprizing both structural and ballistic functions from the same weight.

Better yet if the spacing can facilitate it, would be the addition to the latter of changing the weather deck above it to an armoured deck from a single plate of the minumum de-capping thickness. This would not increase weight (it might even reduce weight) but the effective thickness could be the sum of the new main armoured deck plus the new armoured weather deck. A spaced array requires really two deck spaces between the upper armoured deck and the main armoured deck, with a thin non-ballistic deck in between. However this may not be practical in an existing design.

[Garyt]

Better yet would be the complete removal of the old main armoured deck and structure and replacing it with a single plate of new material comprizing both structural and ballistic functions from the same weight.

Better, but of course more expensive in terms of labor and resources.

Of course, when one looks at the minimal amount gained for adding a second layer, and the added weight causing more fuel to be used and/or lower speed, maybe replacing completely does not look like such a bad idea.

[aurora]

Admiralty drawings of how Hood might have been saved-see post2 in this thread

no21987-1920_Gunnery_trials.jpg (39.03 KiB) Viewed 3167 times

[Garyt]

Interesting. I'd like to run the numbers with Okun's formula to see what that comes up with.

It just seems like 3" of additional deck armor would not be enough if you use the square root of additional layers calculation, as this would give in essence 1.72" of additional protection.

[aurora]

Interesting. I'd like to run the numbers with Okun's formula to see what that comes up with.

It just seems like 3" of additional deck armor would not be enough if you use the square root of additional layers calculation, as this would give in essence 1.72" of additional protection.

Sure is interesting Gary-do publish your findings-I confess Dave had me blinded with science-every day we learn something new.

[Garyt]

Well, Aurora, I'm not sure how much I am on the right track or not

I am not 100% sure as to how much the square root idea is theory and how much of it is proven.

Be interested in any one else thoughts on this matter as well.

[Mostlyharmless]

The square root idea is complete irrelevant as far as the idea of adding a completely new 3 inch (120 lb.) plate to Hood is concerned. The square root calculation assumes that the two plates are parallel. The drawing shows that the shell goes through the nearly vertical 7 inch side plate and then has to pass through the new horizontal 3 inch plate if it is to threaten the magazines. The idea is similar to the protection of Bismarck's machinery by a 145 mm side plate and a horizontal 80 mm deck with a 45 mm or 30 mm bulkhead in between. The shell will be decaped, yawed and critically deflected upwards by the side plate, all of which will help to protect the horizontal deck.

[Garyt]

I guess one question here. Where did the Barbette factor into this? Or was this magazine not protected by the barbette?