The class consisted of five pre-dreadnought battleships of the Imperial German Navy; all ships of the class were named for German emperors. The ships were , , , , and , all built between 1895 and 1901. The class saw the introduction of the traditional armament layout for German battleships prior to the advent of the dreadnought type of battleship in the early 1900s: four large-caliber guns, but of comparatively smaller size compared to their contemporaries, in two gun turrets. The German adoption of smaller guns was a result of a preference for higher volumes of fire over weight of shell. The class also standardized the use of three screws for battleships and introduced water-tube boilers and Krupp cemented armor.
On entering service, the ships were assigned to I Squadron, of which served as the flagship, while served as the flagship for the overall fleet commander. The ships conducted routine training exercises and cruises in the early 1900s and was badly damaged in a grounding accident while steaming in the Baltic Sea in 1901. As newer battleships entered service later in the decade, the ships of the class were moved to II Squadron in 1905 and all of the ships except were rebuilt between 1907 and 1910. Thereafter they were reduced to reserve status beginning in 1908, since more powerful dreadnought battleships had begun to be commissioned; the rest of their peacetime careers consisted of periodic reactivations to participate in annual fleet training maneuvers.
At the start of World War I in July 1914, the ships were recommissioned and assigned to V Squadron; they were tasked with coastal defense in the North Sea but were quickly transferred to the Baltic to support German operations against the Russian Empire. They saw limited activity during this period, and they returned to the North Sea for guard duties in early 1915. The increasing threat of modern weapons, particularly the British submarines that had begun to operate in the area, combined with shortages of crews for more valuable vessels, led the navy to decommission all five members of the class in March 1915. They were used in a variety of secondary roles. They were all discarded in the early 1920s as Germany disarmed under the terms of the Treaty of Versailles.
Design
In the early 1890s, the German Navy attempted to secure funding from the to replace the elderly ironclad , but parliamentary resistance delayed the appropriation until the 1894/1895 budget year. Design studies for the new ship had begun in June 1891 at the request of Kaiser Wilhelm II, and it was quickly decided to make significant changes from the preceding design. The limitations of the fleet's infrastructure, particularly the dry docks and other harbor facilities, along with the Kaiser Wilhelm Canal then under construction, constrained the size of the new ship. To keep the new ship within the displacement limit, the center turret that had been used on the s would have to be sacrificed if a heavier secondary battery was to be incorporated. Five different design sketches were prepared, the first four incorporating a secondary armament of ten guns and eight guns and the fifth replacing the 10.5 cm guns with eight guns. All five variants carried a main armament of four guns. Wilhelm II contributed his own proposal, but it suffered from serious stability problems and was not a serious option.
Work continued on the ships' design while the navy pushed for funding in the , which was finally approved in March 1894, placing pressure on the design staff to complete their work so construction could begin. By May, the design staff had produced sketch XVI, which discarded the traditional two-gun turret used by most navies in favor of four single-gun turrets in the lozenge arrangement used in contemporary French battleships like . If weight permitted, all four were to be 28 cm guns, but the option to reduce the wing turrets to was available if necessary. The secondary battery was to be sixteen of the 10.5 cm guns, with at least some in twin turrets, but over the following months the battery was increased to 15 cm guns, as it was the accepted view at the time that secondary guns would do the most damage in a close-range fight. This view, which advocated the so-called "hail of fire" principle, was seemingly vindicated by the Japanese cruisers' victory over a more heavily armed Chinese fleet at the Battle of Yalu later in 1894. The smaller, faster-firing guns were intended to inflict serious damage on the superstructures of enemy battleships and demoralize the crew.
During the design process, the commander of the Maneuver Squadron, Hans von Koester, suggested that the 28 cm guns be discarded in favor of guns, since they could be fired 2.5 times as fast as the larger guns and they were large enough that they could still be used to penetrate heavy armor at the close battle ranges envisioned at the time. Koester convinced Wilhelm II to overrule the naval high command, who wished to retain the heavier guns. This decision set a pattern of German naval construction for the next two decades that favored lighter, faster-firing guns instead of larger, more powerful ones. Though the decision was criticized at the time on the basis that the 24 cm gun was smaller and thus weaker than the 28 cm, the larger gun offered little substantive advantage at close range, and the much greater rate of fire allowed it to produce a heavier broadside over time.
In August 1894, the navy settled on an ship armed with four 24 cm guns and eighteen 15 cm guns. The decision was a gamble, as Krupp had not actually designed a 24 cm gun, and if the tests had proved to be a failure, the ship would not have had a main battery gun, since her turrets could not be reworked to accommodate the 28 cm gun. The advent of Krupp cemented armor allowed a significant saving of weight, as it was much more effective than traditional Krupp armor, so less armor could be used to achieve the same level of protection. They retained the same armor layout of the s, although the weight savings would have allowed the adoption of a more comprehensive layout that would be used in the subsequent . The propulsion system was improved with the adoption of water-tube boilers and reorganized to incorporate a third propeller shaft, which became standard for German capital ships. The navy had concerns about the reliability of the water-tube Thornycroft boilers, so the first vessel, , was completed with just four of the new types, with the remaining eight being older fire-tube boilers.
After the first vessel was begun, the next member of the class was authorized for the 1896/1897 program; during the intervening two years, consideration was given to re-designing the second ship to match foreign developments, most significantly the adoption of guns like those on the British . The change would have necessitated halving the main battery and the removal of four of the 15 cm guns to offset the weight of the larger guns. Additionally, it would have left with no counterparts, which would have complicated tactical control. The sacrifices were deemed to be too severe, and so the decision was made to go ahead with the 24 cm gun, as successful proof-firing of the new gun had by then been completed.
General characteristics and machinery
The -class ships were long at the waterline and overall. They had a beam of and a draft of forward and aft. The ships displaced normally and up to at full load. The ships' steel hulls were of transverse and longitudinal frame construction. The hull contained twelve watertight compartments and a double bottom that covered 70 percent of the hull. was completed with a tall military mast for her foremast and a pole mainmast. The other four vessels were fitted with short military masts for both masts. In 1901, s foremast was shortened. and , both intended to serve as flagships, were completed with large bridges, with a two-story bridge aboard the former and a single-story bridge on the latter. The remaining three vessels received smaller, open bridges.
The German navy regarded them as having excellent seakeeping. They had a tight turning circle and were very responsive. The ships rolled up to 15° and had a roll period of 12 seconds. They suffered only minor speed loss in heavy seas, but up to 40 percent with the rudder hard over. Their metacentric heights were between . The ships carried a number of smaller boats, including two picket boats, two launches, one pinnace, two cutters, two yawls, and two dinghies. The crew numbered 39 officers and 612 enlisted men. When serving as a squadron flagship, a ship had its crew augmented by another 12 officers and between 51 and 63 enlisted men.
The -class battleships were powered by three 3-cylinder vertical triple-expansion steam engines that drove three screws. , , and were equipped with three 3-bladed screws that were in diameter. and were equipped with two of the 3-bladed screws on the outer shafts and a four-bladed screw that was in diameter on the center shaft. The ships received different boiler arrangements owing to concerns among the naval high command about the reliability of the new water-tube boilers. had an arrangement similar to , except the Thornycroft boilers were replaced by Marine-type fire-tube boilers. and were equipped with four Marine and six cylindrical fire-tube boilers, while had four Thornycroft and six cylindrical fire-tube boilers. All of the ships' boilers were ducted into two funnels, but and had thinner aft funnels while those of the other three ships were identical.
The powerplants were rated at , but on trials could produce up to . This generated a top speed of . The ships carried of coal, although the use of additional spaces within the ships increased fuel capacity to . This provided a maximum range of at a cruising speed of . Electrical power was supplied by five 320 kW 74 volt generators in and , and four 240 kW 74 volt generators in the other three ships.
Armament
The primary armament consisted of a battery of four 24 cm (9.4 in) SK L/40 guns in twin-gun turrets, one fore and one aft of the central superstructure. The guns were mounted in hydraulically operated C/98 turrets, which allowed elevation to +30 degrees and depression to −5 degrees. At maximum elevation, the guns could hit targets out to . The guns fired shells at a muzzle velocity of . Each gun was supplied with 75 shells, for a total of 300.
Secondary armament included eighteen 15 cm (5.9 inch) SK L/40 guns. Six were mounted in single turrets amidships and the rest were mounted in MPL casemates; all were manually operated and elevated. Most of these guns were mounted at upper-deck level, with only four of the casemates at main deck level, which kept them high enough in the ship to avoid a common problem with battleships of the period where heavy seas could make the guns unworkable. According to the historian Aidan Dodson, the arrangement was "perhaps the best of the period." These guns fired armor-piercing shells at a rate of 4 to 5 per minute. The ships carried 120 shells per gun, for a total of 2,160 rounds total. The guns could depress to −7 degrees and elevate to +20 degrees, for a maximum range of 13,700 m (14,990 yd). The shells weighed and were fired at a muzzle velocity of .
The ships also carried twelve 8.8 cm (3.45 in) SK L/30 quick-firing guns for defense against torpedo boats, also mounted individually in casemates and pivot mounts. These guns were supplied with between 170 and 250 shells per gun. These guns fired shell at a muzzle velocity of 590 mps (1,936 fps). Their rate of fire was approximately 15 shells per minute; the guns could engage targets out to . The gun mounts were manually operated. The ships' gun armament was rounded out by twelve Maxim machine cannon.