Prinz Adalbert-class cruiser

Line-drawing of Prinz Adalbert; the shaded areas represent the portions of the ship protected by armor

The ships of the Prinz Adalbert class were 124.9 meters (410 ft) long at the waterline and 126.5 m (415 ft) overall, and had a beam of 19.6 m (64 ft). The ships were designed to displace 9,087 metric tons (8,943 long tons; 10,017 short tons), but at full load displaced up to 9,875 t (9,719 long tons; 10,885 short tons); they had a draft of 7.43 m (24.4 ft) forward and 7.9 m (26 ft) aft. The ships' hulls were constructed from transverse and longitudinal steel frames, over which the steel hull plates were riveted. The vessels contained fourteen watertight compartments and a double bottom that extended for 60 percent of the length of the hull.[4] The designers reverted to the use of two heavy military masts that had been discarded in Prinz Heinrich's design.[5]

The German navy regarded the vessels as good sea boats, with gentle motion when the ships' lower fuel bunkers were full. The ships were responsive to commands from the helm, and steering was controlled with a single rudder. They lost up to 60 percent speed with the rudder hard over, but suffered only minimal speed loss in heavy seas. The ships' casemate guns were placed too low, which rendered them exceedingly wet even in a slight swell. They had a transverse metacentric height of 0.734 m (2 ft 4.9 in). The ships had a standard crew of 35 officers and 551 enlisted men, though when serving as a squadron flagship this could be augmented by another 9 officers and 44 enlisted men. The ships were equipped with several boats, including a pair of picket boats, a launch, a pinnace, two cutters, two yawls, and two dinghies.[6]

Prinz Adalbert and Friedrich Carl were powered by three vertical 3-cylinder triple expansion engines; the center shaft drove a three-bladed screw 4.5 m (15 ft) in diameter, while the two outboard shafts powered four-bladed screws 4.8 m (16 ft) in diameter. The engines were supplied with steam by fourteen coal-fired Dürr water-tube boilers produced by Düsseldorf-Ratinger Röhrenkesselfabrik, which were ducted into three funnels.[4] Compared to those on earlier German cruisers, the propeller shafts were shortened and better faired into the hull lines to reduce the amount of drag they induced, and they were made self-supporting; these changes were incorporated into all future cruisers and battleships built by the Kaiserliche Marine.[5]

The propulsion system was rated at 16,200 metric horsepower (16,000 ihp) for Prinz Adalbert and 17,000 PS (17,000 ihp) for Friedrich Carl and top speeds of 20 knots (37 km/h; 23 mph) and 20.5 knots (38.0 km/h; 23.6 mph), respectively. Both ships reached higher horsepower figures on trials, though their speeds were not significantly improved. The ships were designed to carry 750 t (740 long tons; 830 short tons) of coal, though storage could be increased to 1,630 t (1,600 long tons). This enabled a maximum range of up to 5,080 nautical miles (9,410 km; 5,850 mi) at a cruising speed of 12 knots (22 km/h; 14 mph). Electrical power was supplied by four generators with a total output of 246 kilowatts (330 hp) at 110 volts.[4]

Midsection of Friedrich Carl in a miniature in the Deutsches Museum showing the ship's secondary armament on the side.

Prinz Adalbert and Friedrich Carl were armed with a main battery of four 21 cm (8.3 in) SK L/40 guns in two twin turrets,[lower-alpha 1] one on either end of the main superstructure. The four guns were supplied with a total of 340 rounds of ammunition, or 85 shells per gun. The turrets could depress to −5° and elevate to 30°, which provided a maximum range of 16,300 m (53,500 ft).[4] The 21 cm gun fired a 238-pound (108 kg) shell at a muzzle velocity of 780 m (2,560 ft) per second.[8] The ships' secondary armament consisted of ten 15 cm (5.9 in) SK L/40 guns, all placed in the sides of the hulls. Three guns were mounted in casemates amidships on either side, with a pair of gun turrets above them. These guns were provided with a total of 1,400 shells, or 140 per gun.[4] These guns fired an 40-kilogram (88 lb) projectile at a muzzle velocity of 800 m (2,600 ft) per second. The guns could elevate to 30°, allowing a maximum range of 13,700 m (44,900 ft).[8]

The ships also carried twelve 8.8 cm SK L/35 guns for close in defense; these were arranged in groups of four in shielded pivot mounts. Four guns were mounted around the forward conning tower, four were located around the rear two funnels amidships, with the last four guns placed on top of the rear superstructure.[4] These guns fired a 7 kg (15 lb) shell at a muzzle velocity of 770 m (2,530 ft) per second. They could elevate to 25° and could engage targets out to 9,090 m (29,820 ft).[8] The vessels' armament system was rounded out by four 45 cm (17.7 in) submerged torpedo tubes. They were mounted in the bow, stern, and on each broadside, and supplied with eleven torpedoes.[4]

The steel armor used on the two ships was produced by the Krupp firm. The main belt armor consisted of a layer of teak that was 50 mm (2 in) thick, covered by 100 mm (3.9 in) thick steel plating in the central section, which covered the ships' machinery spaces and ammunition magazines. The belt was reduced to 80 mm (3.1 in) on either ends of the central portion; the bow and stern were unprotected. The armored deck ranged in thickness from 40 mm (1.6 in) to 80 mm. Sloped armor, which ranged in thickness from 50 to 80 mm, connected the deck to the armored belt. The ships' casemate guns, which were placed above the main belt, were protected by 100 mm thick armor plating, as were the 15 cm turret guns. The two 21 cm guns had 150 mm thick sides and 30 mm roofs. The forward conning tower was protected by 150 mm (5.9 in) sides and had a 30 mm (1.2 in) thick roof. The rear conning tower was much less thoroughly protected, with only 20 mm (0.79 in) worth of armor protection.[4]

One of the Prinz Adalbert-class cruisers leading a line of ships

The two ships were re-mobilized after the outbreak of World War I in August 1914. Prinz Adalbert was initially assigned to the IV Scouting Group, and alternated between the North and Baltic Seas for various operations, including cruising with the fleet during the Raid on Yarmouth in early November.[13] Friedrich Carl was sent to the Cruiser Division of the Baltic Sea commanded by Konteradmiral (Rear Admiral) Ehler Behring, where she served as his flagship.[10] The division was based in Neufahrwasser in Danzig. Behring was ordered to attack the Russian port of Libau, which was believed to be acting as a staging area for British submarines. On 17 November, while steaming to Libau, Friedrich Carl struck a pair of Russian naval mines off Memel. The ship's crew managed to keep the cruiser afloat long enough to allow nearby vessels to take off the entire crew; only seven men were killed in the attack. The operation proceeded as planned, however, and several blockships were sunk in the harbor entrance.[14][15]

After the sinking of Friedrich Carl, Prinz Adalbert was transferred to the Cruiser Division and Behring shifted his flag to the vessel.[13][15] The ship conducted several operations against Russian forces in the southern Baltic in the first half of 1915, including bombardments of Libau and supporting minelayers around the Gulf of Riga. She ran aground off Steinort in January but was able to free herself. After repairs were completed, she returned to active duty in March.[16] In May, she supported the German Army attack that captured Libau. On 1 July 1915, the ship sortied to reinforce a German minelaying operation that had come under attack by a Russian cruiser flotilla. While en route with the armored cruiser Prinz Heinrich, Prinz Adalbert was torpedoed by the British submarine E9.[17] The damage was severe, though the cruiser was able to return to Kiel for repairs.[18]

Repairs were finally completed by September 1915. She took part in a sortie into the Gulf of Finland toward the end of the month that resulted in no action. On 23 October, Prinz Adalbert was steaming some 20 miles west of Libau in company with a pair of destroyers when she was intercepted by the submarine E8.[19] E8 fired a spread of torpedoes at a range of approximately 1,200 meters (3,900 ft), which detonated the ship's ammunition magazine.[20] The explosion destroyed the ship, which sank immediately with the loss of 672 crew. There were only three survivors. The sinking was the greatest single loss of life for the German Baltic forces for the duration of the war.[14][19]