Some measure of rectification was seen in the Bellerophon class of 1907, in which particular attention was paid to suitable underwater protection. The screens were extended from ‘A’ to ‘Y’ barbettes and ran down to the double bottom, this forming a continuous anti-torpedo bulkhead that protected not only the magazines and shell rooms, but also the machinery and boilers. This was every bit as good as that fitted in the first two classes of German dreadnoughts (Nassau and Helgoland classes), but this great improvement over Dreadnought was not followed up in British designs, and a return to the small magazine screens was witnessed in the classes from Colossus to Iron Duke (1908–11 designs).
The last two British battleship classes to serve in the war (the Queen Elizabeth and Royal Sovereign classes) were provided with an anti-torpedo bulkhead protection system second to none and easily equal to anything produced for German ships throughout the entire war.
Shortly before the outbreak of war in 1914, work was undertaken to provide British battleships with adequate underwater protection. Experiments were hastily started at Portsmouth and Cambridge test centres. At Cambridge targets of
The Admiralty was aware that the largest torpedo used by the German Navy contained as much as 400lb of high explosive, and a charge of this order was capable of blowing a hole in a steel plate 6in thick. The protection of a ship by underwater armour was, therefore, impracticable because of the weight of armour required. Moreover, it was accepted that at the mean point of impact the ship’s structure would be destroyed over a very large area; with the ordinary plating then in use, it would work out at about 30 square feet. So protection would have to consist of either longitudinal bulkheads strong enough to remain intact and watertight after the explosion, or of an external hull fitting which would cause the torpedo to detonate outside the hull.
Of the two, the first method was the most widely used, and was fitted in its simplest form. The bulkheads were fitted approximately ten feet inboard from the outer hull, the space between being left empty to allow the gases from the explosion to expand and lose pressure and velocity. The problem, however, was that when the hull’s skin plating shattered, the small fragments were projected against the inner bulkhead at a velocity as high as 3,000fps which was capable of piercing up to 2in of steel plate.
Experiments were carried out to full scale on the old pre-dreadnought Hood, which was fitted with various bulkheads and structures on the hull. One test showed that when the space between the outer hull and the inner bulkhead was filled with oil, the fragmentation problem was overcome to some extent. The oil caused the blast pressure to be dispersed in all directions, which pointed to the need to strengthen the transverse bulkheads within the inner compartments of the hull, but in general it was better to have these compartments full than empty.
In August 1915, a possible solution to the problem of underwater defence was seen in a design submitted by Vickers to the Board of Invention and Research for a first class battleship having a speed, armament and above-water armour equal to the latest Admiralty designs, but having in addition an entirely new form of underwater construction for defence against torpedo attack. The novel defensive arrangement in this Design 742 consisted of a strong structural defence in combination with the subdivision of the side compartments in such a way as to allow the expansion of the explosive gases into empty compartments with the minimum of damage. After the gas pressures had diminished they would, in theory, be resisted by strong, circular, outer explosion bulkheads, which were termed the main defence. The arrangement was designed to resist 220lb of gun-cotton detonated against the ship’s side and, pending further investigations, could be made to resist a charge of 400lb. The system was made up of the following components:
1. The shell plating and frames of the ship, reinforced by horizontal timbers.
2. A perforated baffle screen of ¼in nickel steel, reinforced by a central, strong vertical steel stiffener and by horizontal timbers. The screen was approximately six feet from the ship’s outer shell.
3. The interior of each explosion compartment was provided with the above baffle screen which was liberally perforated by 12in diameter holes for the penetration of gases, and arranged so that the screen would, under pressure, fracture gradually.
4. Small transverse oil fuel compartments were placed between the explosion compartments in the wings of the ship in order to add to the oil fuel stowage, with the transverse bulkheads in these compartments so shaped that no direct thrust would be transferred from the outside of the ship onto the main bulkheads.
VICKERS BATTLESHIP DESIGN 742
September 1915
ADMIRALTY PROPOSALS
May 1915
The Board of Invention examined the design and reported to the Admiralty. The design, they reported, differed from existing Admiralty designs mainly in the provision of curved instead of flat bulkheads. The breakdown of inner transverse bulkheads under pressure after being struck was due primarily to the projectile action of fragments of the outer skin. These were sometimes projected with such velocity that bulkheads of up to 2in thick or more became riddled with holes and weakened to the extent that gas pressure could tear large holes in the structure. Vickers’ design would be damaged in the same way. Both the baffle screen and the main defence would certainly be pierced or badly damaged by an explosion, and the system was not viewed as very promising. Concluding remarks from the Assistant DNC, W. J. Berry, summed up the general feeling about the revolutionary system:
On the whole it is considered that the ship proposed would be slightly less vulnerable than the battleships now building, but this is entirely due to the feature of the underwater system being made the principal one. It is probable, however, that further investigations into the problem would result in a superior arrangement being arrived at; but not at the expense of modifying the machinery and armament from existing practice as seen necessary; the extra length, displacement and beam of this ship being accepted as part of the price paid.
Although this novel system of underwater protection was rejected, its submission shows that the problem was understood and a great deal of initiative was being used in an endeavour to come up with an adequate protective barrier against torpedo attack. At the beginning of the war, the need for this type of protection was not paramount in the design, but took second place to armour, armament and speed. Within a few short months, however, it was to become one of the most important features in ensuring a warship’s survival. That the Germans did not feel obliged to enhance their ships’ underwater protection reflects the obvious: their ships’ bulkheads were quite adequate for the job.
Anti-Torpedo