-H.M.S. Hood Reference Materials-
ADM 1-9210: Hood Class: Armour and Deck Protection (1916)
Updated 05-Mar-2010

This document is a modern transcription of Admiralty record ADM 1-9210. It contains correspondence between Director of Naval Construction, Sir Eustace D'Eyncourt and Admiral Jellicoe, concerning Hood's protection and armour. The original file is held at the The National Archives at Kew, London. This Crown Copyrighted material is reproduced here by kind permission of The National Archives.

This is not the complete document, but only a portion. We intend on posting the remainder of the document in the future.

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The following remarks are submitted in connection with the enclosed report:-

2. A drawing is attached showing comparative sections between "X" and "Y" barbettes of the "HOOD" and of the "ROYAL SOVEREIGN". The former ship is very much finer and shallower than "ROYAL SOVEREIGN", and provision has been made for 120 rounds per gun against 80 rounds in the latter ship. A considerable amount of space is also taken up by the shafting. The crown of the magazine is consequentially higher in the "HOOD", but as shown in the armour drawing, a shell would have to penetrate the equivalent of 10.5", and this is considered good and sufficient protection. The additional weight involved in making the crowns of all the 15" magazines 1" thick would be 85 tons; if the crown of the after magazine only, were increased to 1", the added weight would be half the above.

3. It is not seen that the section referred to is "very weak"; a shell would have to penetrate an equivalent thickness of 12" without any addition. The weight involved by the addition shown in green both forward and aft is 30 tons.

The altered protection to the Main Deck referred to at 0 does not involve any additional weight. The original arrangement is considered preferable, as at present the projectile passing through the edge of the Forecastle Deck meets a 120-lbs thickness before it can reach the magazine. The 80-lbs. portion of the deck is behind armour for a 30º projectile.

4 & 5. The arrangement indicated on tracing III is not practicable below the Main Deck. It cannot be carried out in the wake of the forward engine room owing to considerations of space, and any break in the longitudinal continuity of this deck cannot be accepted owing to considerations of structural strength. The proposed method is most objectionable on the score of stability if the belt armour is pierced, and although more effective against projectiles having an angle of descent with the horizontal greater than 15º, would be less effective against projectiles with an angle of descent of less than 15º, i.e., against the very projectiles which would be most likely to perforate the side armour.

With regard to shifting the fore and aft bulkhead between Main and Upper Decks, outboard to cover the electric lead and pipe passage, this would narrow up all the workshops, washplaces etc., on the Main Deck by about 4 feet, and would result in a large amount of wasted space on this deck.

The roof of the passage is covered by 80-lb plating and it will be seen on the section showing this passage, that an equivalent thickness of 14" is obtained through the roof, at 30º angle of descent, so the additional protective plating suggested at III, which involved 110 tons, does not appear necessary.

6. The arrangements proposed are not satisfactory from a strength and stability point of view.

7 & 8. In regard to sudden discontinuity of armour thickness and disposition of the armour thickness according to its distance from the magazine, such discontinuity is a consequence of providing armour protection in thickness adequate for the importance of the part protected.

It is obvious that even in a ship of the "HOOD'S" dimensions, all armour cannot be 12" thick, and it is a sound principle to provide extra thickness at the waterline to protect the stability, thinning it off up the section. The has been an accepted principle ever since armour-clad ship were first designed, and no reason is seen for departing from it. The "HOOD" is very much better protected than any previous ship built or designed for any Navy of which the particulars are known, and the argument that a shell striking above a certain dividing line would do more damage than one just below the line, does not appear to carry any weight.

If the 12" belt were stopped at the Main Deck level and the middle tier of armour tapered, from 11" at the Main Deck to 5" at the Upper Deck, see section herewith, no additional weight of armour is involved, but the increased cost would amount to £20,222 per ship with considerably increased time of manufacture. Further, it is always found in practice, that a tapered plate is inferior in resistance to attack to a parallel plate of the same weight, so that any apparent advantage on paper would be lost in practice.

As at the worst place just at the top of the 12" belt, there is a minimum equivalent thickness of 12.5" for the shell to penetrate, the extra cost, time and difficulty in working is not thought worth while.

11. A report received from "REPULSE" (D.09020/16) does not bear out these remarks. On the contrary, the flare has been proved to have realised all that was expected at the Admiralty for it.

It is pointed out that the work is proceeding on the lines originally approved, as also the drawings of structural arrangements which take considerable time to prepare. The arrangements were all most carefully considered in the design stage, having in view not only the protection, but also strength, stability and structural convenience, points which, especially as regards strength and stability, have been to a great extent overlooked in the proposals under consideration.

If any or all of the above alterations were to be made, it would be desirable that an early decision should be given and communicated to the Firms.

A print and tracings, 2 in No. are attached illustrating the above remarks.

E d'Eyncourt

DNC 9 Dec 1916

 

SECRET

"IRON DUKE"

7 November 1916.

No.2632/H.F.175.

Sir,
With reference to Admiralty letter of 20 October 1916, S.01750/16, In regard to the protection of H.M.Ships of the "HOOD" class, be pleased to lay the following report before the Lords Commissioners of the Admiralty.

2. The crowns of "X" and "Y" magazines are only 16 feet from the upper deck, compared with a distance of 23 feet in "IRON DUKE" and "ROYAL SOVEREIGN" classes.

A shell penetrating the upper deck will probably not burst until it reaches the thick main deck. Shell splinters in this case will certainly penetrate the crowns of the magazines.

It is therefore considered that Crowns should be thickened by an additional 40 lbs.

3. Similar increases in thickness of Crowns over "A" and "B" magazines is recommended.

The section shown in the Admiralty sketch "Before the centre of "A" Barbette" is very weak, and it is considered that

(a) the lower deck between station 67 and the transverse armour should be increased by 40-lbs;
(b) the longitudinal magazine bulkhead should be thickened in this vicinity.

It would appear also that a more uniform protection to the magazines would be obtained if the main deck between the knuckle lines were made everywhere 100 lbs, instead of 120 lbs, and 80 lbs as at present.

4. A better protection to the boiler rooms, and the fore and aft communication passage, is shown in Tracing III. The increase of weight for the length of the boiler rooms is 65 tons. In ships of the "QUEEN ELIZABETH" class a shell penetrating the 240-lbs side armour, just under the main deck, has almost free access to the communications passage. (The roof is only 40-lbs distant 16 feet from the ship's side.)

5. The sloped deck immediately behind the armour presents a normal surface to shells striking the ship at an angle of approximately 25º. The internal protective bulkhead should be placed vertically, and continued if possible in line with the internal torpedo protective bulkhead. Tracings I and II show the proposed modifications abreast the forward and after magazines. These proposals do not involve and increase in weight.

If it is found impossible to modify the sloped deck in the "HOOD" class, then it is considered essential that slope be increased in thickness to 120-lbs for a depth sufficient to allow of shell penetrating just above the main armour belts at angles of up to 30º.

6. The disposition of protective plating in the vicinity of the water line is not always arranged in the best possible manner. Especially is this the case in ships of the "ROYAL SOVEREIGN" class. Sections between "X" and "Y" barbettes have been prepared showing

(a) Existing construction;
(b) How a more adequate protection of the magazines and water plane is attained without any increase in weight. A shell penetrating the main belt and bursting inside will certainly penetrate the sloped armour deck. Even if the shell bursts outside the main belt, or in passage through, the sloped deck will be distorted, owning to its close proximity to the ship's side at the outboard end.

7. Disposition of the armour in all classes of ships show sudden discontinuities, which are fatal to adequate and uniform protection of the vitals. In the case of a ship of the "HOOD" class for instance, two shells striking the ship, one at the top of the main armour belt, the other just above it, strike at points practically eqi-distant from the magazines. Yet one shell has to penetrate 5 inches more armour than the other. Embrasures and deck spaces between transverse armoured bulkhead are other weak spaces.

8. Armour on the ship's side should taper according to the distance from the nearest point of the magazine, or other vital element being protected, or what is practically the same thing as the distance from the water line. If this proposal is carried out, the water plane will also be protected in the best possible manner. The increased cost of the tapered armour must be accepted.

9. Distance of magazines from the ship's side appears to have been neglected in the disposition of the protective material.

10. The following is a summary of the proposed armour modifications for the "HOOD" class:-

(i) The crowns of the magazines to be increased by an additional 40-lbs.
(ii) Main deck between the knuckle lines over forward magazines to be of uniform thickness of 100-lbs.
(iii) Lower deck forward and the longitudinal magazine bulkhead to be thickened by an additional 40-lbs.
(iv) Sloped deck in the vicinity of boiler rooms, magazines, etc., to be altered as proposed in tracings.

11. The flare forward in the design of the "HOOD" class appears to be excessive. Reports on this subject have been called for from "REPULSE", as it is believed that in that ship the flare has proved to be excessive and has given rise to difficulties.

12. It is observed that proposals regarding Conning Towers recently put forward are not embodied in the design of the "HOOD" class.

I am, Sir,
Your obedient servant,
[signed] J Jellicoe ADMIRAL