Kaiser-class battleship

Initial designs

Development of the Kaiser class began in early 1908 with the German Kaiserliche Marine (Imperial Navy) in a difficult position. The first two classes of dreadnought battleships ordered by Germany—the Nassau and Helgoland classes—had sharply increased in cost over earlier pre-dreadnought battleships, and the Reichstag (Imperial Diet) had begun to question the spiraling costs. At the time, Admiral Alfred von Tirpitz, the state secretary of the Reichsmarineamt (RMA—Imperial Naval Office), had recently secured parliamentary approval for the 1908 amendment to the Naval Law, but objections to the rising naval expenditures soon began to mount. The situation was exacerbated by criticism from retired naval officers such as Vice Admiral Karl Galster, who opposed Tirpitz's plans and preferred a smaller and more defensively oriented fleet based on cruisers for trade protection and commerce raiding coupled with torpedo boats and submarines for defense of Germany's coastline. The situation was to an extent moot, as the Naval Law already fixed the schedule of battleship construction, and the 1908 amendment reduced the replacement age of existing battleships from 25 to 20 years, so the six Siegfried-class coastal defense ships, the two Odin-class coastal defense ships, and as the four Brandenburg-class battleships would have to be replaced.

Tirpitz nevertheless proceeded with development of a successor to the Helgoland class, requesting new proposals from the Construction Department of the RMA on 15 May 1908, before work on the preceding battleships had even begun. He instructed the staff to use the same armor layout and boilers as Helgoland, but they should substitute new steam turbines for the triple-expansion steam engines used in the earlier vessel. The position of the secondary armament was to be raised to reduce the potential for flooding through the gun ports in the event of underwater damage or severe listing. The number and arrangement of main battery guns was a topic for open discussion. By early June, the department had prepared five options, designated "1a", "1b", "1c", "2", and "3". Details of the latter two have not survived, but the first three were variations on the same general arrangement: two superfiring main battery gun turrets forward, another superfiring pair aft, and two wing turrets placed amidships; the primary difference between the three versions was the height at which the secondary guns were mounted and the amount of freeboard.

The question of cost once again intervened in the form of a general budget crisis in the German government, and Tirpitz was compelled to agree to keep the price of the next class of battleships at the level approved for Helgoland. He was now confronted with the possibility of repeating the Helgoland design for the next four-ship division of battleships or reducing the armament of the new ships to retain the turbines, which were significantly more expensive than the older steam engines. Hans Bürkner, the chief naval architect, proposed reducing the number of main guns from twelve to ten, which would reduce prices to an acceptable level, though Tirpitz was adamantly opposed to the idea. Consideration was given to deleting cruising turbines, but this was estimated to reduce the ship's range by up to 25%, and it could not be remedied without unacceptable increases to the ships' size and draft to accommodate larger coal storage bunkers. Instead, Tirpitz asked Bürkner to prepare a variant of "1c" with a more closely arranged secondary battery, which would shorten the area needed to be protected with armor, and would thus save weight. The result was labeled "1c2", and was completed in August and approved by Tirpitz in September.

Another major problem loomed: the British Royal Navy was rumored to be developing a new 34.3 cm (13.5 in) gun to arm the successors to HMS Neptune, and the level of armor protection adopted for "1c2" was inadequate to protect the new ship from these larger British weapons. This led to the development of two new versions by October, "1c3" and "1c4", which traded lighter armor at the bow and stern for suitable levels of armor protection in the citadel. The latter also incorporated a raised forecastle to improve seakeeping. By this time, renewed political opposition to further increases in naval spending came from Chancellor Bernhard von Bülow and Reinhold Sydow, the finance minister. Tirpitz was accordingly forced to abandon his objection to Bürkner's proposed solution, and ten-gun-armed designs began to be evaluated by December 1908.

Finalizing the design

The Construction Department prepared a total of nine 10-gun variants in late December 1908; these were numbered from 8 to 16. Each variant adopted different arrangements of the main battery turrets, including a combination of centerline turrets, some in superfiring arrangements and others not; wing turrets either in en echelon arrangements or abreast of each other; and even two proposals that had two twin-gun turrets placed side-by-side forward, like the old Siegfried-class coastal defense ships. Before any of these proposals was selected for further development, Tirpitz met with Kaiser Wilhelm II on 14 January 1909 to secure approval to reduce the armament from twelve to ten guns. Wilhelm II agreed, but mandated that the decrease in offensive power must be balanced by an increase in defensive qualities.

Tirpitz soon settled on two designs, "8" and "16", for further development, which produced "8a" and "16a". Both of these used a similar arrangement of the main guns: one turret forward, two wing turrets en echelon, and two more in a superfiring pair aft. The chief difference was that "16a" was slightly longer, which gave enough room to space the wing turrets far enough apart that they were able to fire to either broadside over limited arcs. The weight savings from the sixth turret was used to increase belt armor from 300 to 340 mm (11.8 to 13.4 in) in thickness, and to extend the height of the belt. He took both designs to Wilhelm II for review on 27 January. Wilhelm approved "16a" to be developed into the new battleship. The Construction Department objected to the selection, citing the asymmetrical arrangement of the guns, though they were overruled by the General Navy Department of the RMA, which pointed out that the battlecruisers of the Von der Tann, Moltke, and Seydlitz classes used the same en echelon pattern.

Bürkner presented a refined proposal, "16a mod", on 16 March; the primary changes being another increase in length coupled with a slightly narrowed hull to improve its hydrodynamic efficiency. This also allowed the casemate battery to be spread out and created room for another boiler. Several major details remained to be decided, however, including the arrangement of the propulsion system. Bürkner suggested a four-shaft set of Parsons turbines, though included an option for a three-shaft system using AEG turbines. During a meeting on 30 March, representatives of the General Navy Department presented criticisms, citing what they expected to be insufficient freeboard, the mounting of 8.8 cm (3.5 in) guns atop the wing turrets (a British practice they disliked), and the suggestion that the wing turrets receive fewer shells but would be able to share between their magazines. Another meeting on 7 April was spent evaluating "16a mod" for minor cuts to various aspects to reduce the expected displacement from 24,500 to 24,280 metric tons (24,110 to 23,900 long tons; 27,010 to 26,760 short tons).

As the Construction Department continued to refine the design, it was discovered that the buoyancy of the propeller shafts equated to about 230 t (230 long tons; 250 short tons) of displacement, which allowed several of the reductions imposed in April to be reversed. The thickness of the belt armor was also increased to 350 mm (13.8 in). On 1 September, the RMA sent the finalized criteria to the various German shipyards to solicit bids. Initially, four vessels were authorized on 30 September, though the propeller arrangement was still not settled at this late date. The issue was finally resolved in a pair of meetings on 22 and 27 October, and Tirpitz ultimately selected the three-shaft system. Next, on 23 November, Tirpitz requested a study to evaluate the possibility of drastically revising the armament for the next battleship—designated "Ersatz Odin"—to use triple turrets. The Construction Department quickly pointed to several problems, namely the significant cost of developing the new turrets, problems with supplying the center gun, and difficulties with fire-control practices. Next, the designers evaluated the possibility of keeping all five turrets on the centerline, as was by then standard British and American practice. The studies eventually led to the follow-on König-class battleships, but the anticipated delays in designing the new ships led Tirpitz to order Ersatz Odin as a fifth Kaiser-class ship.

Diesel engines

Representatives for Maschinenfabrik Augsburg-Nürnberg (MAN) gave a presentation in the Reichstag proposing the adoption of diesel engines for future battleships. Shortly thereafter, the Construction Department evaluated the idea, and Admiral Max Rollmann stated the engines would have several benefits over traditional coal-fired boiler and turbine systems. These included significant reductions in weight of the system and the number of men needed to operate them, since stokers would no longer be needed. In addition, exhaust gases would be much reduced, which meant that fewer funnels would be needed, thereby decreasing the ship's size as a target. Counted against these improvements were two major drawbacks: coal bunkers were an integral part of a ship's protection scheme, so there would be a loss in defensive capabilities, and the engines were very tall, which would require alterations to the deck armor. The other major issue confronting the German naval planners was the untested nature of diesel engines that large, though MAN agreed to build a testbed engine at its own expense.

Rollmann recommended accepting the proposal, and Tirpitz inquired as to whether the first two ships could be redesigned to include the new engine on their central propeller shafts (while retaining turbines and boilers on the outboard shafts). The Construction and General departments rejected the idea, since work on the turbines had already begun, and any change would involve delays and increased costs that the navy was unable to bear. These costs were in part the result of a need to redesign the turbines to increase their power to allow the ships to reach their intended maximum speed without the diesel engine. It was ultimately decided that the last vessel, Ersatz Odin, would be fitted with the engine on an experimental basis. It was not ready by the time the ship was completed, however, since repeated problems with the testbed engine required significant alterations and redesigns. In addition, the outbreak of World War I in July 1914 forced the designers to switch from standard diesel fuel to tar oil, since Germany lacked ready access to petroleum products. The finalized engine was not ready to be installed until mid-1918, but the ship could not be taken out of service to have it retrofitted due to the ongoing conflict.