Mackensen-class battlecruiser

The Mackensen class was the last class of battlecruisers to be built by Germany in World War I. The class was to have comprised four ships: Mackensen, the name ship, Graf Spee, Prinz Eitel Friedrich, and Fürst Bismarck. None of the vessels were completed, as shipbuilding priorities were redirected towards U-boats. They were broken up in the early 1920s.

The design of the Mackensens was a much improved version of the previous. They featured a new, more powerful 35 cm (13.8 inch) gun. The Mackensen-class ships featured more powerful engines that gave the ships a higher top speed and a significantly higher cruising range. The Mackensen design provided the basis for the subsequent, which incorporated even larger 38 cm (15 inch) main-battery guns, as a response to the Royal Navy's s. These last three ships are referred to as the Ersatz Yorck class, as the first ship of the class was designed to replace the armored cruiser SMS Yorck, which had struck German mines early in the war and sunk. However, very little construction progress was made on these later ships.

In response to the Mackensen-class ships, the British laid down the s for the Royal Navy, all but one of which would eventually be canceled; the sole survivor, HMS Hood (51), was completed after the end of the war.

Design
The fourth and final Naval Law, passed in 1912, governed the building program of the German navy during World War I. The Navy Office decided the Navy should construct one battleship and one battlecruiser every year between 1913 and 1917, with an additional unit of both types in 1913 and 1916. By February 1915, the German High Command had realized that the war would not be won with a lightning campaign as in 1870. Therefore, the Navy department decided to replace the six armored and seven light cruisers that had been sunk by that point in the war. Kaiser Wilhelm II requested the new ships be armed with 38 cm (15 inch) guns; Admiral Friedrich von Ingenohl, the commander in chief of the High Seas Fleet, preferred the 30.5 cm gun of the preceding Derfflinger-class ships. As a compromise, the new battlecruisers were to be armed with eight 35 cm (13.8 inch) guns.

The design staff was generally in agreement with the standard practice of using coal-fired boilers for two-thirds of the power plant, with the remainder being oil-fired boilers. Coal-fired boilers were preferred because the coal, stored in the sides of the ship, provided additional protection, particularly for the battlecruisers. There was a problem with any enlargement of the new ships over the preceding designs. The Imperial dry docks were only deep enough for ships with a draft of 9 m. This meant that an increase in displacement would necessitate a longer and wider hull. This was compounded by restrictions on width imposed by the locks of the canal in Wilhelmshaven.

General characteristics
The Mackensen-class ships were 223 m long, had a beam of 30.5 m, and a draft of 9.3 m forward and 8.4 m aft. The ships were designed to displace 31000 MT on a standard load, and up to 35300 MT fully laden. The Mackensen's hulls were composed of longitudinal steel frames, over which the outer hull plates were riveted. This was the same type of construction as in the preceding Derfflinger-class battlecruisers, and was intended to save weight compared to the traditional method of construction, which incorporated both longitudinal and transverse frames. The ships' hulls contained 18 watertight compartments and a double bottom that ran for 92% of the length of the hull. This was significantly greater than the older Derfflinger-class ships, which had a double bottom for only 65% of the length of the hull.

The ships as designed required a crew of 46 officers and 1,140 enlisted sailors. Service as a squadron flagship would increase that number by an additional 14 officers and 62 sailors. The vessels carried a number of small boats, including two picket boats, one barge, two launches, two cutters, and three yawls.

Machinery
The ships of the Mackensen class were equipped with four sets of marine-type turbine engines, each of which drove a three-bladed screw that was 4.2 m in diameter. The turbines mounted in Fürst Bismarck were equipped with Föltinger fluid transmission, while those on the other three ships were two sets of direct coupled turbines with geared transmissions. The ships had 24 coal-fired marine-type single ended boilers and eight oil-fired marine-type boilers. The power plants were designed to provide 90,000 shaft horsepower and 295 revolutions per minute. Maximum speed was rated at 28 kn. The vessels were designed to store 800 MT of coal and 250 MT of oil in purpose-built storage spaces, though the hull areas between the torpedo bulkhead and the outer wall of the ship were used to store additional fuel. Maximum fuel capacity was 4000 MT of coal and 2000 MT of oil. This was estimated to give a range of up to about 8000 nmi at a cruising speed of 14 kn. Electrical power on the vessels was provided by eight diesel generators that put out 2,320 kilowatts at 220 volts. The ships were equipped with a pair of rudders mounted side by side, as opposed to the tandem rudders used on the Derfflinger-class ships.

Armament
The Mackensens were equipped with a main battery of eight new 35 cm (13.8 inch) SK L/45 guns in four twin gun turrets. The turrets were mounted in superfiring pairs fore and aft of the main superstructure. The guns were placed in Drh LC/1914 mountings, which could elevate to 16 degrees and depress to −8 degrees. The guns were supplied with a total of 720 armor-piercing shells, or 90 per gun. The weapons were designed to fire 600 kg (1,323 lb) shells at a rate of fire of around 2.5 shots per minute. The shells were fired with a muzzle velocity of 815 meters per second (2,674 f/s). As with other heavy German guns, these weapons used a fore propellant charge in a silk bag with a main charge in a brass case. These guns could hit targets out to a maximum distance of 20,000 m (21,870 yards).

The ships' secondary battery consisted of fourteen 15 cm (5.9 in) SK L/45 quick-firing guns mounted in armored casemates along the central superstructure. Each gun was supplied with 160 rounds, and had a maximum range of 13,500 m, though this was later extended to 16,800 m. The guns had a sustained rate of fire of 5 to 7 rounds per minute. The shells were 45.3 kg (99.8 lb), and were loaded with a 13.7 kg (31.2 lb) RPC/12 propellant charge in a brass cartridge. The guns fired at a muzzle velocity of 835 meters per second (2,740 ft/s). The guns were expected to fire around 1,400 shells before they needed to be replaced.

The ships were also armed with eight 8.8 cm (3.45 in) L/45 Flak guns in single pedestal mounts. Four were arranged around the rear superfiring main battery turret and the other four around the forward conning tower. The Flak guns were emplaced in MPL C/13 mountings, which allowed depression to −10 degrees and elevation to 70 degrees. These guns fired 9 kg (19.8 lb) shells, and had an effective ceiling of 9,150 m at 70 degrees.

As was standard for warships of the period, the Mackensens were equipped with submerged torpedo tubes. There were five 60 cm tubes: one in the bow, and two on each flank of the ship. The torpedoes were the H8 type, which were 8 m long and carried a 210 kg (463 lb) Hexanite warhead. The torpedoes had a range of 6,000 m (6,550 yd) when set at a speed of 36 knots; at a reduced speed of 30 knots, the range increased significantly to 14,000 m (15,310 yd).

Armor
The Mackensen-class ships were protected with Krupp cemented steel armor, as was the standard for German warships of the period. The armor layout was very similar to the armor scheme on the preceding Derfflinger-class ships. They had an armor belt that was 300 mm thick in the central citadel of the ship, where the most important parts of the ship were located. This included the ammunition magazines and the machinery spaces. The belt was reduced in less critical areas, to 120 mm forward and 100 mm aft. The belt tapered down to 30 mm at the bow, though the stern was not protected by armor at all. A 45 mm thick torpedo bulkhead ran the length of the hull, several meters behind the main belt. The main armored deck ranged in thickness from 30 mm thick in less important areas, to 80 mm in the sections that covered the more critical areas of the ship.

The forward conning tower was protected with heavy armor: the sides were 300 mm thick and the roof was 130 mm thick. The rear conning tower was less well armored; its sides were only 200 mm thick and the roof was covered with 50 mm of armor plate. The main battery gun turrets were also heavily armored: the turret sides were 270 mm thick and the roofs were 110 mm thick. The 15 cm guns had 150 mm worth of armor plating in the casemates; the guns themselves had 70 mm thick shields to protect their crews from shell splinters.

Construction and cancellation
Four ships were planned in the class: Mackensen, Graf Spee, Prinz Eitel Friedrich, and Fürst Bismarck. Mackensen—ordered under the provisional name Ersatz Victoria Louise—was named after Field Marshal August von Mackensen. The ship was laid down 30 January 1915 at Blohm & Voss in Hamburg, under construction number 240. She was launched on 21 April 1917, but construction was halted about 15 months before she would have been completed. Mackensen was stricken from the German navy, according to the terms of the Treaty of Versailles, on 17 November 1919. She was sold for scrap and eventually broken up in 1922 at Kiel-Nordmole. Graf Spee was named for Vice Admiral Maximilian von Spee, the commander of the German East Asia Squadron; he was killed when his squadron was annihilated at the Battle of the Falkland Islands in 1914. Graf Spee was laid down 30 November 1915 in the Schichau yards in Danzig (now Gdańsk, Poland), under the provisional name Ersatz Blücher. She was launched on 15 September 1917. Construction stopped about 12 months away from completion; Graf Spee was the furthest along of all four ships when work was halted. She too was struck on 17 November 1919; on 28 October 1921 the unfinished hull was sold for 4.4 million Marks and broken up in Kiel-Nordmole.

Prinz Eitel Friedrich, ordered as Ersatz Freya—a replacement for SMS Freya, was named for one of Kaiser Wilhelm II's sons, Eitel Friedrich. She was laid down on 1 May 1915 at Blohm & Voss under construction number 241. She was 21 months away from completion when she was launched to clear the slip on 13 March 1920 and was broken up at Hamburg in 1921. At the launching ceremony, dockyard workers named the ship Noske, after Reichswehr Minister Gustav Noske. Fürst Bismarck, ordered as Ersatz A, was named for the famous German chancellor Otto von Bismarck. The ship was laid down on 3 November 1915 at the Kaiserliche Werft Wilhelmshaven under construction number 25. She was about 26 months from completion when work ended. She was never launched; instead, the vessel was broken up on the slip in 1922.

The primary reason construction halted on the four ships was the shifting of ship building priorities from capital ships to U-boats. In the last two years of the war, what little resources were available to the navy were directed towards U-boat construction; this caused a shortage of construction materials and slower build times for large warships. The RMA filed a report dated 1 February 1918, which stated that capital ship construction had ground to a halt, primarily due to the shifting priorities to the U-boat war.