SMS Derfflinger I

Length: 210m

Beam: 29.0m

Draught: 9.20m

Displacement: 26.600 tonnes

Armament: 8-30.5cm L/50

12-15cm L/45

12-8.8cm

4-50cm torpedo tubes

Speed: 26.5 knots

Range: 5.600nm at 14 knots

Design

In mid-April 1910 the (K I E) – the design section (E) of the construction department’s shipbuilding section (K) I – requested that the General Navy Department, (A), set out the specifications for the battleships and cruisers of 1911, so that building documents could be prepared and other preparations could begin. (A) replied on 16 April 1910 and said that it was ‘inappropriate at this point in time’ to set specifics. They pointed out that: the firing trials of Nassau were yet to be considered; the triple turret project, only begun by Krupp briefly before, required further work; and the results of trials of the large diesel engines, under development by Maschinenfabrik Augsburg–Nürnberg (MAN) and the Germania Shipyard, which would provide the first solid grounds for assessment of this engine type, would only be known early in the winter of 1910.

Nevertheless, Vizeadmiral Paschen of (A) pointed out in his proposals for the Großen Kreuzer 1911: ‘that the new English battlecruisers have been confirmed as mounting 13.5in guns, so that a calibre increase to 10–30.5cm is unavoidable. The difference of shell weight – 302kg against 600kg – becomes too large.’ He said the construction must include ten 30.5cm in either a centreline or diagonal disposition, and that a diesel engine should be installed on the centre shaft of a three-shaft arrangement. There should also be improved underwater protection, among other things.

At the same time the State Secretary, Admiral von Tirpitz, arranged the first of a series of meetings for all parties regarding the questions of armament and propulsion for the four ships in the 1911 budget. At this meeting on 11 May 1910 Kontreadmiral Gerdes, from the weapons department (W), introduced the results of the latest firing trials and performance diagrams of 28cm, 30.5cm and 32cm guns, which gave a comparative examination of the projectile effect at long ranges. With a battle range of 8,000–10,000m and an assumed armour thickness of 250mm for the newest Royal Navy cruisers, Kontreadmiral Gerdes believed the 28cm gun was no longer sufficient for Großer Kreuzer K, especially as the cruiser was later expected to fight in the line of battle against battleships, with an armour thickness of 300mm. The increase in weight of eight 30.5cm guns compared to the artillery of J was a modest 36 tonnes, including an increase in turret armour.

Admiral von Tirpitz held a contrary view and could not foresee a battle range of 10,000m or more, and even if fire was opened at such a great range he believed it would quickly reduce. He believed the real duel would occur at shorter range and that for this five 28cm double turrets would be more appropriate. He left no doubt that this was his preferred option. Finally, he questioned those present as to their opinion on the question of calibre. Vizeadmiral Paschen, of the General Navy Department, (A), professed himself in support of five 28cm turrets – which was somewhat surprising in light of the memorandum from (A) that ten 30.5cm SK were recommended. The representative of the constructon department, (K), Vizeadmiral Rollmann, had spoken up for five 28cm turrets, though without explanation.

State Secretary Admiral von Tirpitz concluded the exchange of views regarding armament by saying that he had ‘temporarily’ decided in favour of five 28cm double turrets. He did not believe that the time had come for an increase in cruiser calibre, even if the battleships had received heavier guns. He believed a more favourable time for an increase would be the following year, 1912, when just one battleship keel would be laid down and more funds would be available for the cruiser.

Nevertheless, Tirpitz considered the question of the propulsion system even more important than armament. On 6 May, at the first meeting about the 1911 ships, he had stated: ‘… the construction of the 1911 ships with diesel engines is the most important of all, and the principal decision now is to solve construction questions.’ He saw the installation of diesel engines as a chance ‘for a real leap ahead of other navies’, and ‘all other (questions) fade into the background.’ However, there were some with reservations and Baurat Bürkner and Hüllmann wanted time to develop suitable underwater protection, and reiterated that the change to diesels would place a great burden on the construction department. Considerable changes to the battleship type being built at the same time would be necessary and were likely to cause delays. Tirpitz was aware of the risk of proceeding without sufficient investigation but there was already a substitute solution for K: she would be constructed as a sister ship of J.

The construction department did not believe a design with five 28cm turrets and diesel engines to be the most advantageous and therefore during the following weeks (K I E) was asked to examine alternatives. To rationalise this work an adaptation of J-designs could be used and the rejected 1910 cruiser projects IIIc and IVe were again taken from the filing cabinet. By the end of May a design with four 30.5cm turrets en échelon had been produced and a month later a design with the same in a centreline arrangement. The state secretary now gave up his insistence on 28cm calibre, but the preference for diesel engines remained.

The chief of KII, the Construction Department for Engine Installations, Geheimrat Veith, had been cooperating since 1909 with the firm MAN on the development of large diesel engines. On 28 February 1910 a contract was signed between the RMA and MAN for an experimental 6,000hp three-cylinder motor. However, at a meeting on 1 September Geheimrat Veith stated that the development of large diesel engines for cruiser K was ‘not yet ripe’ to consider instalment. Bürkner and Veith also rejected the employment of a diesel on the centre shaft alone on the same basis. Consequently, the cruiser of 1911, and likewise the new battleships, would be powered by turbines alone.

The 1 September meeting also sought to remove doubts about calibre. A memorandum from the meeting dated 2 September noted: ‘the großer Kreuzer K to receive 30.5cm as heavy armament in four double turrets. His Excellency the Herr State Secretary wants the opportunity to go to five 30.5cm double turrets, should this be considered.’ This was rejected on the grounds of displacement and cost increases, and also, curiously, because it was still believed there should be a difference in armament between battleships and cruisers. The memorandum continued: ‘the centreline position should be used for the four twin turrets, if the second and third turrets can fire over the first and fourth turrets, so that four heavy guns can fire directly ahead, just as directly astern. If this is not quite possible, the von der Tann arrangement should be taken up.’

A memorandum of 22 September 1910 put forward three designs with differing turret positions so that a decision on turret placement could be made. Whilst it was noted that all three were ‘feasible’, Bürkner gave preference to design 2, or design 3 if its higher cost was acceptable. The main features – engine performance, speed and coal provisions – were the same as cruiser J, as was the armour thickness. The armament and turret and barbette armour were improved. Design 1 had the turrets arranged in en échelon positions and the upper deck was carried through to the stern. Design 2 showed the aft turrets in the arrangement accepted later, somewhat separated. The outboard turbines were situated beside C turret, and the inboard turbines were between C and D turrets, giving the characteristic gap between the turrets. This arrangement saved one compartment length. Design 3 positioned the 15cm guns on the upper deck, set back from the hull side, and positioned the aft turrets in the classical super-firing arrangement. None of the designs showed a forecastle, but each had a gently ascending fore deck, just as Moltke. The munition outfit was assumed as ninety shots for each 30.5cm, 160 shots per 15cm and 250 shots per 8.8cm gun.

On the recommendation of Bürkner, design 2 was changed to incorporate the higher-positioned 15cm battery, as with design 3, and the subsequent design 4 was approved by the Kaiser on 26 September. The centreline arrangement of the turrets received the Kaiser’s blessing.

After further improvements and accurate estimations, the final form, design 4b, displaced 25,900 tonnes. Nevertheless, on 18 March 1911 (K I E) proposed a further improved design, design 5. For the same displacement and cost, this design showed many improvements. In the midship area the Zwischendeck was omitted, allowing a greater compartment height above the armoured deck, therefore permitting the upper coal bunker capacity to be increased to in excess of 4,000 tonnes without restricting the accommodation space for the crew. The lower hulls of both 4b and 5 were to be constructed with a pure longitudinal frame system to increase the hull unit strength whilst maintaining the desired weight. The distance between frames would now amount to 640mm instead of 1,200mm. The partitioning of the boiler rooms would again be into two with a middle longitudinal bulkhead, similar to design IVc for cruiser J, and von der Tann. Therefore there would be 2+2+2+2+2+2 boiler rooms with 2+4+4+4+4+4 boilers. It was planned to employ the large capacity double boilers first trialled with von der Tann and have twenty-two boilers with a grate area of 266sq m. This would give a speed the same or higher than cruiser J.

With the dimensions chosen for design 5 the stability was high with a metacentric height of 2.7–2.9m, and an expected roll period of ten and a half seconds. Some of the reasons for a high metacentric height, and hence great stability, were from a desire for the heeling moment during a turn to be small so the lower edge of the belt did not rise above the water, and also to reduce the danger of capsizing when damage occurred. For example, filling one engine room and nearby wing cells only caused a list of 7½°. However, ships with a large metacentric height possessed a characteristic quick and severe roll-correcting impulse and so their roll period was short. This had a disadvantage in that the armament required as stable a platform as possible. To reduce the metacentric height of design 5 to 1.6–1.8m would require a reduction in beam of about 2m, so that the distance from the torpedo bulkhead would be reduced from 4m to 3m and the protection of the ship against underwater weapons would be correspondingly reduced. This consideration, and the fact that the specific wave frequency in the North Sea favoured a large metacentric height, led (K) to consider the installation of Frahm roll-damping tanks, just as had been installed aboard von der Tann, although they were against any other reduction in stability such as through reduction of the beam. The other alternative, bilge keels, would cause a slight loss in speed. To install the Frahm system, the citadel would have to be lengthened by 3m and consequently the displacement would increase by about 300 tones, with an increase in cost of approximately half a million marks, including licensing fee. The construction department, (K), recommended the acceptance of project 5, but the General Navy Department, (A), were against it.

Under these circumstances a further conference was convened to iron out the differing views of (K) and (A), and a record of the 30 March meeting gives an interesting insight into the workings of the RMA and the various personalities concerned. Those present were: His Excellency the Herr State Secretary, Admiral Tirpitz, Admiral Gerdes, Admiral Rollmann, Vizeadmiral Paschen, Korvettenkapitän von Trotha, Geheimrat Veith, Geheimrat Bürkner, Geheimrat Hüllmann and others. The meeting began with Admiral Tirpitz asking what Krupp had said about the various designs, and he was given the answer that they were for design 4 in preference to design 5. However, as design 4b had the same problems as design 5, Krupp’s concerns could be disregarded. Admiral Tirpitz favoured design 5 because it had a higher freeboard.

Geheimrat Bürkner then explained that the finished work on the design would require an increase in weight to 26,900 tonnes. He said the casemate had been moved outboard at the request of the General Navy Department. Other improvements included a conical shape for the forward barbettes and an increase in height of turret IV by about 0.2m; better protection of the turret substructure; increasing the armoured deck above the 15cm gun munition chambers to 50mm and increasing the armour thickness of the conning tower substructure to 200mm, all of which would bring about a weight increase of about 150 tonnes. However, Admiral Tirpitz rejected these improvements because of the increase in cost involved. He then asked what weight reductions could be made. Admiral Paschen replied that the torpedo bulkhead could be reduced 5mm in thickness to 45mm, but Tirpitz objected to this as it reduced the protection against torpedoes. Geheimrat Bürkner then suggested a reduction in the thickness of the bow armour and Admiral Tirpitz said the question to be answered was whether to move the casemates of design 4b outboard, or reduce the thickness of the torpedo bulkhead or bow armour to save weight. Admirals Tirpitz and Gerdes were against reducing the bow armour as it provided protection against medium calibres, and heavy calibres would only leave medium calibre-sized holes.

There was then a debate about the effect of detonating shells on and inside the hull. Geheimrat Hüllmann then said: ‘One must expect that the ship will fill with water forward. Leaks will occur that cannot be sealed with the means available onboard,’ and then: ‘The ship’s outer hull, to which the armour is secured, will undoubtedly leak, and the forecastle ahead of the citadel will certainly fill, and could not be kept drained with the means available onboard.’ With remarkable prescience, Geheimrat Hüllmann was describing almost exactly what was to happen to Lützow five years later. The discussion continued about reducing the armour forward and the weight saving this would achieve, and then went on to the question of roll-damping tanks and the weight increase this would bring. His Excellency the Herr State Secretary then decided that the Frahm roll-damping be provided, the ship’s weight be increased by approximately 300 tonnes and that the casemates should be moved outboard, whilst the thickness of the torpedo bulkhead should be reduced to 45mm. Geheimrat Veith then remarked that 80 tonnes weight could be saved by substituting oil-fired boilers for some of the coal-fired boilers.

On 15 June the Construction Department presented a memorandum with proposed improvements for the final model of design 5b. Design 4 had the casemate positioned one deck higher than design 5 and the space between the citadel and the casemate was protected by just 150mm of armour, which was considered a weakness. So the casemate was brought down one deck and the heavy armour then reached the Batterie deck. The silhouette of the ship was also reduced. The bow armour immediately ahead of the citadel was reduced in height. The casemates were moved outboard to the hull side to increase the seaworthiness of the ship. They were also lengthened to allow two more 15cm guns, or the installation of Frahm roll-damping tanks. The forward conning tower substructure was reinforced similarly to that of battleships. The torpedo bulkhead was reduced from 50mm to 45mm thickness. The gun turrets received a splinter shield between the guns and there were to be four 50cm torpedo tubes. The boiler plant was divided into two, which allowed better smoke extraction, less space loss in the upper decks and the possibility of arranging a bunker inside the torpedo bulkhead. The question of some boilers being purely oil-fired was put to one side. The lower hull was to be constructed with a pure longitudinal frame system, which saved weight. Because of these improvements the displacement increased by 700 tonnes to 26,600 tonnes and the length and beam were slightly increased. The Kaiser subsequently approved this design.

On 30 June 1911 the question of oil firing was given further consideration. First, the advantages of oil-fired boilers were given. In comparison to coal boilers they had less weight and smaller dimensions for the same performance; they were easier to serve and there were not inconsiderable savings in personnel, coal trimmers and stokers; furthermore, steam could rapidly be raised, and oil firing was smoke-free, thereby avoiding the telltale smoke column. On the other hand (K) feared the stoppage of boilers should the oil run out. Furthermore, it was feared the storing of oil would be difficult because of the potential failure of oil-tight riveting, and it was thought that oil was ‘a danger for the ship’. (K) also took the view that coal provided protection and that with an increasing shortage of oil it would have to be acquired from foreign suppliers – especially in times of crisis – and this would be very difficult. Nevertheless, the report concluded that eight of the single coal boilers would be replaced by four double-ended oil-fired boilers and that 600 tonnes of oil would be accommodated in the double bottom and 400 tonnes in trim cells. The coal provisions would be reduced to 3,200 tonnes and with the oil this would correspond approximately to the previous coal provision of 4,600 tonnes.

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