Introduction.—The idea that the 10,000-ton, 8-in.-gun treaty cruisers ought to be conceived, designed, and built as pocket battle cruisers, has germed simultaneously on both sides of the Atlantic. In the U.S.A., the thought was put forward by Professor Hovgaard, and in Holland by the present author.
Some treaty cruiser development in the direction of increased protection followed, but not nearly as radically as had been advocated. With the world on what looks very much like the verge of another war, the author decided to dig up his pocket battle cruiser from his archives and to have another look at it. The result of that overhaul is now presented, and Fig. 1 shows the proposed general arrangement.
So 30 knots with full load, i.e., nearly 31 knots in mean war condition, would suffice against almost any of these, with the exception of the French Dunkerque- Since 20 years of service should be expected from a 10,000-ton cruiser, and capital ship construction has been started afresh by the French initiative, we must consider whether the capital ships of the future may be battleships or battle cruisers. Or, putting it another way, whether a satisfactory 16-in.-gun battle cruiser, having a speed of over 30 knots and its protection determined by the necessity to be able to lie in the line against 16-in.-gun battleships, could be built within 35,000 tons displacement.
The fundamental idea of this preliminary design is that the ship is built to serve the gun, and that that gun is ill- served should the hull be blown away below it. So the hull is entitled to be protected for its own sake and not merely fitted with protection to the so-called vitals. In fact, in an artillery ship buoyancy and stability ought to be protected against the attack of the guns of similar ships. This is what Professor Hovgaard has termed the principle of corresponding protection.
Protection nowadays is to be fitted against submarine dangers as well as against gunfire. The latter may be said to be chiefly a question of weight, but the former is primarily a question of space. And on that score, under-water protection is a still more tricky problem in so relatively small a vessel as a treaty cruiser is. In face of the old problem of putting a quart into a pint pot, lower limits had to be fixed for the speed and for the main battery.
Speed.—The lower limit for speed was found by requiring the ship to be able to keep contact with any adversary of the treaty-cruiser class for a sufficient time to inflict such damage to these under-protected vessels as to effect, at least, a reduction of the opponent’s speed so as to prevent her escape. It was considered that this requirement could still be satisfied by a speed not less than 29 knots in a fullload condition of 14,000 tons.1 But to begin with, a speed of 30 knots in full-load condition was laid down for the design This speed was checked against battlecruiser speeds, which are as follows for ships in service and building:
Kongo class |
Japanese (after refit) |
26 knots |
Hood |
British |
31 |
Renown, Repulse |
British (after refit) |
30 |
Deutschland class |
German |
26 |
Dunkerque |
French |
32 (?) |
So 30 knots with full load, i.e., nearly 31 knots in mean war condition, would suffice against almost any of these, with the exception of the French Dunkerque. Since 20 years of service should be expected from a 10,000-ton cruiser, all" capital ship construction has been started afresh by the French initiative, we must consider whether the capital ships of the future may be battleships or battle cruisers. Or, putting it another way, whether a satisfactory 16-in.-gun battle cruiser, haying a speed of over 30 knots and its protection determined by the necessity to be able to lie in the line against 16-in.-gun battleships, could be built within 35,000 tons displacement.
Evidently, the answer is in the negative, as proved by the 41,500 tons of the 15-in.- gun Hood. The Dunkerque should be underprotected, if one may judge her from the analysis of Obermarinebaurat Evers in the German periodical Werft-Reederei-Hafen of 1933. Herr Evers bases his study on such information as had become available at the time of writing, and credits her with eight 13-in. guns and 9-in. side armor. This is nearly exactly the same as the battle cruisers of the Queen Mary type.
On the other hand, it is not possible to obtain more than 30-knot speed in a 10,000-ton cruiser without affecting the defensive qualities, since the engine weight required would impair the protection against gunfire, while the space needed for the power plant would not leave enough room for the explosion chambers of the under-water protection.
We therefore decided not to sacrifice the good defensive qualities of the armored 10,000-ton type (which enable her to deal with ships of her own class far better than would a few additional knots) to a somewhat better chance of escape in an encounter with one of the very few existing battle cruisers with speeds of or above 30 knots. For such an emergency, we decided upon a torpedo armament of two quadruple mountings, so as to have a weapon with which to strike at opponents twice or thrice her size. In a retreat before a battle cruiser, the length of torpedo run would be much below actual fighting range, and salvos of torpedoes could be counted upon to present a chance of hits.
Main battery.—As to caliber, there is not much to choose: the 8-in. gun is, apart from treaty restrictions, well-nigh the standard cruiser gun of the period. Reduction in armament for the sake of better protection is to be sought exclusively in decreasing the number of guns.
Since efficient gunnery requires salvos of at least three guns, an arrangement of six guns in two triple turrets, one forward, one aft, would be the lower limit of armament. Thus, efficient ahead and astern fire is retained. Mounting the six guns in three twin turrets will always result in a considerable arc of fire where only two guns can be brought to bear.
Moreover, a 3-turret arrangement will j take up nearly 50 per cent more space in the fore-and-aft direction. If under-water I protection is insisted upon, this means serious encroachment upon deck space available for the secondary armament, which must be fitted between the heavy turrets or turret groups, in order to leave the arcs of fire of the main armament entirely free.
The well-known objection of putting too many eggs in one basket should be countered by good armor protection, which becomes all the more feasible when the number of turrets is diminished and high super-firing barbettes with their concomitant heavy armor weights are no longer retained. Ammunition stowage was allotted at 200 rounds per gun.
Under-water protection.—This is largely a matter of beam. In the present case, it was found possible to devote 14-9" on each side to this use, out of a beam of 65'-7". The remainder may accommodate engines, boilers, and magazines by accepting German standards of compactness, though an American-trained mind might prefer to call these “standards of congestion.” But there is no choice.
The protective layer width available is blow U. S. standards, but above pre-war German ones, as evidenced by Fig. 2. The arrangement adopted may be termed an attempt at making an “oil edition” of the German coal protection arrangements. Placing the armor bulkheads in the absorbing structure was not undertaken on account of the restricted width of the protective layer as a whole; it was feared that an unarmored flooding boundary bulkhead at only 15 feet from the ship’s side would fall an easy victim to flying fragments, if not to the violence of the explosion itself. Therefore, the flooding boundary was designed as a cofferdam, consisting of an armored outer bulkhead of 1.57-in. (40 mm.) thickness, supported by 2-ft. web frames on its inside. The inner flange material of these webs, regarded ns beams against such explosion pressures ns may remain after having demolished the absorbing structure, was disposed in the form of a continuous W. T. bulkhead forming the flooding boundary proper.
It is realized that the real protective value of the arrangement can only be ascertained by means of explosion tests, but even if these would not result in a complete resistance to mine and torpedo, a considerable advantage would already be gained if the protective layer succeeded in substituting flooding only to wholesale destruction of vitals.
The size of the protective bunkers and explosion chambers will, of course, have to be decided upon with due regard to oil fuel stowage.
The protective layer should present a Uniform width from top to bottom and from end to end as much as possible. The former requirement can only be met by adopting a nearly rectangular midship section, and the latter by resorting to a fairly full form for the ship as a whole. Together, both compel the designer to adopt lines not conducive to minimum resistance. About 4,000 s.hp. were sacrificed in this way, but the extra machinery weight is, °f course, at least partly compensated for by the gain in hull and armor weight coming from the smaller principal dimensions of the fuller ship.
Nevertheless, the V-type after lines make an inclined position of the torpedo bulkheads in way of the aft magazines and shellrooms unavoidable, and even so these had to be restricted to the platform deck. The forward magazines are on the platform deck as well, but the shellrooms had to be placed on the inner bottom, which is raised in these regions.
Beyond the magazines are situated the handling rooms of the turrets, in order to gain space on deck for the secondary armament. This, however, was not done before a study of the magazine and shellroom layouts had indicated that a satisfactory supply of ammunition could be reckoned with, though at the cost of increased space for transport.
Pending definite information on the protective qualities of the arrangement as suggested, a center-line bulkhead had to be adopted in order not to lose both engine-rooms through a single torpedo hit in way of them. The dangers of such a bulkhead were quite realized and large stability was adopted as a counter-measure.
Above-water protection.—This was arranged on the raft body system and designed to keep out as far as possible 8-in.-A.P. shells at normal impact at a range of 10,000 meters (nearly 11,000 yards). According to a statement made in 1928 by Messrs. Bofors, Sweden, this would require 6-in.-Krupp armor on the sides, as well as 2-in.-K.N.C. armor on the decks in horizontal position. In his paper, Professor Hovgaard strikes a more optimistic note.
It was ultimately decided to have a 5½- in. belt all along the vitals, also enclosing the thwartship protective layers at the ends of the citadel. The advantage of including barbette armor in the thwartship armor bulkheads was thus sacrificed, but by this means the under-water protective layer is shielded against gunfire all around. The thickness of 5½ in. was a compromise between the conflicting claims of having 6-in. armor on the sides, and the necessity of providing a good height of belt. A reasonable armored freeboard had to be provided as a complementary measure to fitting under-water protection. The amount of reserve buoyancy protected is shown in Fig. 3, and the list and sinkage resulting from one torpedo hit are shown in Fig. 4 for four conditions of loading. Flooding was assumed to affect the largest compartment in the ship, viz., the turbine-room, the adjoining condenser room on one side, as well as part of the cofferdams, protective bunkers, and explosion chambers, as shown in Fig. 5.
It is seen that in the intact condition good margins of freeboard are still available for another hit on the same side, but as far as armored stability is concerned, this could not be achieved on the small displacement.
The 2-in.-armor deck would be in danger of being pierced by an 8-in.-A.P. shell striking at the moment of a roll toward the enemy. For this contingency, a 1-in.- splinter deck was added below, in one plane with the whaleback armor decks at the ends. It was realized that heavier plating would be better suited for this splinter duty, but on the restricted weight this could only have been done at the expense of the armor deck. And while this procedure may have something to commend itself in all cases of penetration, the heavy upper armor deck is superior against all semi-A.P. and H.E. shell fire.
The double protective deck should also afford a certain degree of protection against aerial attack.
The ends of the ship have been given some slight protection in the form of 1-in. outside plating in the region of the water line, in addition to the 2-in. whaleback armor decks. For rudders, the semi-balanced skeg type was chosen, in order to avoid the necessity of having a rudder bearing on the under side of the armor deck, which is apt to jam at the first hit upon that deck in the region.
Turret protection was kept at 6 in., but the conning tower was protected by 8-in. armor, which should be able to stand normal impact of 8-in.-A.P. shell at 8,000- meter (8,800 yards) range. Thus, the main battery may seem somewhat under-protected in comparison to the sides. This objection is acknowledged, and calculations showed that another 135 tons of armor would be needed to provide 8-in. thickness on the gun positions. This could be achieved within the 29-knot speed limit, but was not included in order not to overstate the case. However, the 6-in.-turret armor was arranged all round the turrets and barbettes, no reductions having been allowed for sides and backs. Inclined roof plating was taken at 5.1 in. and horizontal roofs at 4 in. Turret fronts were taken at 8 in., but more in the nature of compensation for the weakening caused by the gun ports.
Between the armor and splinter decks, the heavy barbettes were enclosed by 2-in. splinter plating.
The location of the splinter deck, 10 in. above the full load water line, is rather on the high side. This could not, however, be avoided with a view to the space required by the machinery. Moreover, with present-day, long-range firing and its concomitant relatively steep angles of projectile descent, location below the water line is no longer a protection in itself. And anyhow, if any reduction in the height of engines, boilers, etc., were practicable at all, it could only be accomplished at the expense of the space required by the under-water protection. So the high position of the splinter deck was arrived at as a compromise between the conflicting claims of the two types of protection.
The 4.7-in. anti-destroyer guns (see below) were protected by means of 2-in. turret plating, so as to shield the gun crews from casualties that might otherwise be inflicted by attacking destroyers using their guns as well as their torpedoes in the hope of defeating the destroyer defense by means of the splinter effect of their shells.
Secondary artillery.—On a 10,000-ton cruiser, the secondary guns proper (as distinct from A.A. machine guns) should be made to serve the dual purpose of heavy anti-aircraft as well as anti-destroyer guns. American practice is to fit a 25-caliber, 5-in. gun, thereby giving precedence to the claims of A.A. fire. For anti-destroyer duties, a 40- or 50-caliber gun would be preferable, and as to caliber, 5 in. is preferred in the U. S. Navy, while European opinion favors 6 in.
The biggest “long” guns for A.A. practice are of 4.7-in. bore, as fitted in the British battleships Nelson and Rodney, as well as in Japanese ships. From measurements from sketches, these guns appear to be about 40-45 calibers in length.
European treaty-cruiser practice generally favors the 4-in. caliber, but as an anti-destroyer gun this was already given up before the war. A compromise had therefore to be adopted, and as such the 4.7-in. caliber was chosen. This may be termed the standard destroyer gun of the period and as such may be expected still to have sufficient power against that type of ships, though it is on the light side. For length, the general arrangement plan allows for 50-caliber barrels, so as not to underestimate the claims made upon deck space.
The secondary battery was divided in two groups. The forward group is mainly anti-destroyer battery (though fitted with high-angle mounts), and consists of six 4.7- in. guns in two triple turrets, one on each beam just abaft the arcs of firing of the forward heavy gun station. The aft group is stationed on a deckhouse just in front of the aft heavy gun station and, from considerations of space, it had to be restricted to one triple mounting. Ammunition was allotted at 250 rounds per gun.
The heavy A.A. battery was supplemented by eight 1.57-in. (40 mm.) machine guns for close range work, mounted in two groups of four on the upper deck port and starboard. For these, 1,000 rounds per gun are allowed. Eight 50-in. machine guns with 2,500 rounds each are also allowed for, but are not shown on the plans.
All light gun ammunition is concentrated in two magazines at the ends of the machinery spaces. This necessitates longitudinal transport, which would be arranged between the armor and splinter decks. The 4.7-in.-gun turrets have splinter-proof barbettes down to the armor deck.
Torpedoes.—Under-water torpedo rooms always present weak spots in the watertight subdivision and, moreover, the danger of explosion of own torpedoes as a consequence of enemy torpedo hits. That would send the ship to her doom at once and was therefore not allowed. Deck mountings were the only alternative. Space could be found for the two quadruple 21-in. mountings already mentioned.
Aircraft.—The ship being designed to suit the main 8-in. armament, the allowance of aircraft has been made more in the nature of what could be carried on the remaining deck space than on any other grounds. With the torpedo tubes in the wings, one center-line catapult was all that could be fitted, with two planes in addition; one plane to be carried on the catapult, and the other on the deckhouse abaft the single funnel.
Airplane sheds could be considered either on the spot of the after deckhouse, or in a common structure with the funnel The former position would cause great expenditure of weight in devising a sufficiently stiff base for the triple 4.7-in. gun, which would then have to be raised on top of it, and ammunition supply to that gun would become difficult. In addition, such a shed would form a high and massive after superstructure, which in conjunction with the forward deckhouses and mast would greatly facilitate course estimating by enemy gunners. In one block with the funnel, the airplane sheds would probably interfere with due mounting of the A.A- machine-gun batteries. Putting the latter on top of the shed would, again, present munition supply puzzles.
Extra deck space could not be obtained without moving the heavy gun stations farther to the ends of the ship, which would weaken the under-water protection to their magazines in the rapidly narrowing transverse sections. Moreover, greater distance of heavy turrets would mean greater weight of raft body armor, which could not be spared.
Commanding stations.—These include an armored conning tower, a fire-control top having splinter protection, and an unprotected A.A. control position on the deckhouse aft.
The conning tower has 8-in. armor on the sides and 4-in. roof. No communication tube is provided, since the low position of the tower made it preferable to put it right on top of the armor deck. It presents a navigating compartment of horseshoe shape as well as a central gunnery control station on a somewhat higher level. The two are separated by means of a splinter bulkhead.
The control top is a 2-deck structure with 2-in. splinter plating and 2-in. communication tube down to the splinter deck.
Right below the mast is the transmitting station, where also the cables and voice pipes from the conning tower are led. The passage of these cables and tubes through the space between armor and splinter deck is protected by 2-in. plating.
A good space had to be left open between conning tower and mast, since the tower-mast type of structure would otherwise obstruct too great an arc of horizon for the conning tower. As it is, the 15-ft. range finder on top of the latter has a blind arc of 60 degrees, while outlook aft from the navigating compartment was obtained to within 4 degrees of the fore-and- aft line.
Rolling tanks.—The armored stability can only be provided by means of ample metacentric height, which varies from 5 feet at standard displacement to 7 feet in full load condition. Even taking into account the damping power of the 1,200 tons of armor on the sides, this is likely to result in excessive rolling, if no countermeasures are taken. As such, rolling tanks must be included in the design, to be Worked with fuel oil. From German data, it would appear that these were a standard feature of the light German warships of the war period. The tanks should be provided for from the very first stages of design.
Reducing the metacentric height to minimize rolling would not be a satisfactory solution, since this would mean sacrificing one fighting value, i.e., stabilty against bilging, to another, i.e., steadiness for efficient gunnery. As a matter of fact, the whole of the armor weight would at once be depreciated in value, if the ship should not have adequate battle stability.
Principal dimensions.—These will be stated in feet and inches as well as in metric units, in which they were computed. In case of any small difference between the two sets of figures the metric ones are authentic.
Length on L.W.L.. |
179.50m |
588'-ll" |
Breadth on outside of armor... |
20.00m |
65'- 7" |
Depth molded...... |
11.50m |
37'- 9" |
Draft, full load..... |
6.25m |
20'- 6" |
Draft, standard (mean) |
4.77 m |
15'- 8" |
Freeboard, mean war condition, forward |
7.70 m |
25'- 3" |
Freeboard, mean war condition, amidships |
5.99m |
19'- 8" |
Freeboard, mean war condition, aft |
6.65 m |
21'-10" |
S.hp.................... |
|
75,000 |
Speed, full load... |
|
30 knots |
Speed, mean war condition.... |
|
30.7 knots |
Speed, standard displacement.. |
|
31.5 knots |
As far as could be judged from published photographs, the freeboard amidships in mean war condition is about the same as that of the later British treaty cruisers.
Weights.—These have been allotted as follows (all tons metric):
The H-type PBC. |
|
|
Tons |
Hull without light armor contributing to strength |
3,175 |
Light armor incorporated in strength hull |
1,475 |
|
|
Structure |
4,650 |
Hull auxiliaries |
370 |
Inventory and outfit |
430 |
|
|
Hull complete |
5,450 |
Hull armor not contributing to strength |
1,509 |
Fixed armor for battery |
286 |
Revolving armor for same |
330 |
Armament without armor |
1,065 |
Propelling machinery with auxiliaries |
1,520 |
|
|
Standard displacement |
10,160 |
Fuel oil and reserved feed water |
3,840 |
|
|
Full load displacement |
14,000 |
This estimate has been based on careful study and comparison of every bit of information available on warship weights, and most of it comes from the Nachrichtenüber den Kriegsschiffbau (Notes on Warship Construction) in the German periodical Werft-Reederei-Hafen. The armor weights were computed from a set of tentative lines.
A comparison with the Houston type of U. S. cruisers may be of interest. Published information states these ships to have finished some 700-900 tons below the standard weight of 10,000 tons (of 2,240 lb.). This would at once make the difference between the 5½ -in.-armor belt on the H-type and the 3-in.-protective plating on the sides of U. S. ships. Cuts in offensive power would include 32,000 s.hp., one triple 8-in.-gun turret with protective plating, two planes and a catapult, while also the superstructures have been strongly reduced.
The armor deck of the H-type would, on account of its elevated position in the ship and continuous construction for more than 60 per cent of the length, be able to take over strength-deck duty and enable heavy topside plating to be omitted.
Strict economy of weight would, of course, be necessary, but that is a feature of all really modern warship design.
Acknowledgments.—The author’s best thanks are due to Captains J. J. M. Baart, Royal Dutch Navy (Ret.), late chief of the Bureau of Ordnance of that Navy, and C. E. L. Helfrich, R. D. N., late chief of Naval Staff in the Dutch East Indies, for their enthusiastic co-operation throughout the work.
Summary.—No better summary can be given than that of Professor Hovgaard’s 1929 paper:
“She would be a dreaded enemy of the present treaty cruisers and of all smaller light warships, as well as all merchant vessels.”
Every commander tries to get the initiative. He wants to have the first move. The reason is that the enemy must reply to your move, and in order to reply must first find out what your move was, what you have done. To find that out is the chief difficulty in war. Wellington once said that he had spent his time for years trying to get to know what was going on on the other side of a hill- Sherman described a general’s chief anxiety as caused by '‘what he can’t see the enemy doing." The commander who has the initiative throws this difficulty on to his opponent, and in general the initiative is with the attacker. I say in general, because the attacker may lose this advantage by a false move; probably if neither side made any mistake—which is out of the question—the attacker would always have the initiative. Troops, it is generally believed, prefer to attack. The men are said to dislike the suspense of waiting for the enemy.—Wilkinson.
Editor’s Note.—Figures 1, 2, 3, 4, and 5 in this article are reproduced by courtesy of The Shipbuilder and Marine Engine-Builder.
1. All tons are metric throughout the article; 1 ton of 2,240 lb. = 1.016 metric tons.