The class was a class of three battlecruisers of the German (Imperial Navy). The ships were ordered for the 1912–1913 Naval Building Program of the German Imperial Navy as a reply to the Royal Navy's two new s that had been launched a few years earlier. The preceding and the incrementally improved represented the end of the evolution of Germany's first generation of battlecruisers. The class had considerable improvements, including a larger primary armament, all of which was mounted on the centerline. The ships were also larger than the preceding classes. The class used a similar propulsion system, and as a result of the increased displacement were slightly slower.
The class comprised three ships: , , and . All three of the ships saw active service with the High Seas Fleet during World War I. was commissioned shortly after the outbreak of war, and was present at most of the naval actions in the North Sea, including the battles of Dogger Bank and Jutland. was commissioned in August 1915, and participated only in the raid on Yarmouth before being sunk at Jutland. was commissioned into the fleet in May 1917, and saw no major action. and were interned at Scapa Flow following the armistice in November 1918. Rear Admiral Ludwig von Reuter, who was in command of the interned High Seas Fleet, ordered the ships to be scuttled in an attempt to prevent their possible seizure by the Royal Navy.
Development Background Discussions began in April 1910 over the basic design requirements for the next German battlecruiser, which was to follow . The Construction Department's design section requested general specifications in mid-April, but the General Department replied that it was too early. They cited the fact that the s had not yet completed firing trials and other design projects—such as a triple gun turret and a large diesel engine—were still in very early stages of development. At the same time, the General Department's (VAdm—Vice Admiral) Adolf Paschen noted that the British Royal Navy had increased the caliber of its battlecruisers' main battery from to , and so the Germans would need to increase their own from to 30.5 cm. He also argued that the propulsion system should be changed from four to three screw propellers, with the center screw powered by a diesel engine for improved fuel economy.
Admiral Alfred von Tirpitz, the State Secretary of the (Imperial Naval Office), convened the first of a series of meetings to discuss the next battlecruiser design at around the same time as the discussions between the Construction and General departments. The first meeting, held on 11 May, examined the results of recent firing tests of the 28 and 30.5 cm guns, along with that of an experimental gun. (Rear Admiral) Gerhard Gerdes, a member of the Weapons Department, stated that expected battle ranges of , the 28 cm gun would not be able to penetrate the armor of the latest British battlecruisers, which was believed to be thick. Tirpitz argued that fighting would take place at much closer distances, ranges at which the 28 cm gun could still penetrate armor of that thickness. Paschen and VAdm Max Rollmann, the latter from the Construction Department, also voted for the 28 cm gun, which Tirpitz announced was at least temporarily the selection.
Tirpitz next pressed the question of the ship's propulsion system; he strongly favored the adoption of diesel engines, which he saw as a way to take a significant qualitative step ahead of foreign navies that still relied entirely on steam turbines. The naval engineer Hans Bürkner opposed the measure, given the untested nature of the new engine (and associated risks should the project fail), along with the excessive workload that would be created for the design staff, since they would need to redesign the underwater protection scheme and other aspects of the hull. The designers suggested that simply ordering the next cruiser, provisionally titled "K", as a sister ship to . The final decision on diesel engines, either as the sole engine type or as part of a mixed installation with turbines, was forced after the head of the Construction Department's propulsion section informed the naval leadership on 1 September that the diesel engine being developed by MAN AG would not be ready for "K".
Design preparation Detailed design work began soon after the initial discussions in early 1910. The design staff started with abandoned proposals for , projects "IIIc" and "IVe"; the former was a four-turret-armed ship equipped with 30.5 cm guns and the latter carried ten 28 cm guns in five turrets, all of which were mounted on the centerline. In June 1910, a third alternative that combined the two variants—four 30.5 turrets on the centerline—was produced. By that time, Tirpitz was convinced that the larger gun was preferable. The decision was formally adopted in a meeting on 1 September, which was memorialized by Tirpitz the following day. In the memo, he expressed a preference for two superfiring pairs, one forward and one aft, but conceded that if this were impossible, an offset wing turret arrangement as used in the battlecruiser would be acceptable. He also indicated that a fifth turret should be incorporated if weight and cost limits could be met, though such an increase proved to be prohibitive by both metrics.
On 22 September, Bürkner submitted his evaluation of three different proposals, designated 1, 2, and 3. The first used the arrangement for the main battery, while the latter two used the centerline layout. The primary differences between 2 and 3 were the spacing of the rear pair of turrets (2 being placed close together, while 3 increased the distance) and the placement of the secondary armament; 2 raised the secondary guns to the upper deck. All three proposals maintained the same level of armor protection as in , along with speed and coal provisioning. Bürkner recommended design 3, but with the raised secondary battery as in 2; this refined design was then designated 4, which Kaiser Wilhelm II approved on 26 September. Further detailed improvements produced design 4b.
On 18 March, the design staff presented design 5, which included a number of internal improvements over 4b. One of the internal decks was removed from the central portion of the ship, which allowed greater space for coal storage. The designers also adopted a new construction technique to save weight. Previous battlecruisers were built with a combination of transverse and longitudinal steel frames; the -class ships dispensed with the transverse frames and used only longitudinal ones. This enabled the ship to retain structural strength and a lower weight. Lastly, because of the internal reorganization, the boiler rooms could be divided by an internal bulkhead that reduced the risk of flooding in the event of underwater damage. Large capacity double-ended boilers that had been tested aboard would also be used, which should provide the ship with the same speed as or better.
Design 5 had one significant drawback; the ship's metacentric height would have been around , which was too high, as it would have caused the ship to roll too quickly. The fast roll period would have degraded the gunners' ability to aim their weapons. The beam could be reduced by about , but this would corresponding reduce the space between the outer hull and the torpedo bulkhead, which would have worsened the ship's resistance to underwater damage. Frahm anti-roll tanks were also considered, but these would have caused an increase in displacement and cost. Another conference was held on 30 March 1911 to evaluate the proposals, along with ideas to save weight to accommodate the anti-roll tanks. Among the options considered were a reduction in the thickness of the torpedo bulkhead or the bow armor, and the substitution of some oil-fired boilers for coal-burning boilers.
A finalized version, 5b, was completed on 15 June. The changes from design 5 included the reduction of the torpedo bulkhead and lowering the height of the bow armor, but not the adoption of partial oil firing for the boilers. In addition, the secondary battery was lowered by a level and brought to the edges of the hull, which had the effect of improving the ship's seakeeping. Displacement had increased from about , and the hull had been slightly lengthened and widened to accommodate the additional weight. Wilhelm II approved the design soon thereafter. On 30 June, the naval leadership met again to discuss oil-burning boilers; those in favor argued that they were lighter and easier to operate, which would afford a significant reduction in crews. Those opposed cited the difficulty in obtaining fuel oil, especially in a crisis, and that coal storage bunkers provided protection that oil tanks could not. The conference participants concluded that eight of the twenty-two boilers should be oil fired. They also decided to install the Frahm anti-roll tanks, despite the fact that tests aboard revealed they only reduced rolling by about 33%.
The -class battlecruisers were ordered under the fourth and final Naval Law, which was passed in 1912. Tirpitz used public outcry over the British involvement in the Agadir Crisis of 1911 to pressure the Reichstag into appropriating additional funds to the Navy. The Fourth Naval Law secured funding for three new dreadnoughts, two light cruisers, and an extra 15,000 officers and men in the Navy for 1912. The three dreadnoughts secured in the bill became , , and . In the meantime, pressure from the British public and media had forced the British Parliament to step up ship building. Kaiser Wilhelm II requested that the build time for the new battlecruisers be reduced to two years each, as opposed to three years. This proved unfeasible, because neither the armor or armament firms could supply the necessary materials according to an expedited schedule.
Design General characteristics
and were long at the waterline and long overall. was slightly longer, at at the waterline and overall. All three ships had a beam of , and a draft of between forward and aft. The first two ships were designed to displace with a standard load, and up to at combat weight. displaced slightly more, at standard and fully laden. The ships' hulls were constructed from longitudinal steel frames, over which the outer hull plates were riveted. s hull contained sixteen watertight compartments, though and had an additional seventeenth compartment. All three ships had a double bottom that ran for 65% of the length of the hull. This was a decrease from preceding German battlecruisers, which had a double bottom for at least 75% of the hull.
The ships were regarded as excellent sea boats by the German navy. The -class ships were described as having had gentle motion, though they were "wet" at the casemate deck. Steering was controlled by a pair of rudders placed on the centerline. The ships lost up to 65% speed with the twin rudders hard over, and heeled up to 11 degrees. This was greater than any of the preceding battlecruiser designs, and as a result, anti-roll tanks were fitted to . the tanks were tested at sea in December 1914 with inconclusive results. The three ships had a metacentric height of . The standard crew for one of the vessels was 44 officers and 1,068 men; when serving as the flagship for the I Scouting Group, the ships carried an additional 14 officers and 62 men. The s carried smaller craft, including one picket boat, three barges, two launches, two yawls, and two dinghies.
Machinery