Derfflinger-class battlecruiser

SMS Derfflinger
Class overview
Name	Derfflinger
Operators	Imperial German Navy
Preceded by	SMS Seydlitz
Succeeded by	Mackensen class
Built	1912–1917
In service	1914–1919
Completed	3
Lost	1
General characteristics
Type	Battlecruiser
Displacement	26,600 t (26,200 long tons) normal load 31,200 t (30,700 long tons) full load
Length	210.40 m (690 ft 3 in) overall
Beam	29 m (95 ft 2 in)
Draft	9.20 m (30 ft 2 in)
Installed power	14 coal-fired boilers 8 oil-fired boilers 62,138 shp (46,336 kW)
Propulsion	2 sets steam turbines 4 × screw propellers
Speed	26.5 knots (49.1 km/h; 30.5 mph)
Range	5,600 nmi (10,400 km; 6,400 mi) at 14 knots (26 km/h; 16 mph)
Complement	44 officers 1,068 enlisted men
Armament	8 × 30.5 cm SK L/50 (12"/50 cal) guns 12 × 15 cm SK L/45 (5.9"/45 cal) guns 12 × single 8.8 cm (3.5"/45 cal) guns 4 × 50 cm (19.7") torpedo tubes
Armor	Belt: 100–300 mm (3.9–11.8 in) Turrets: 270 mm (10.6 in) Conning tower: 300 mm
Notes	[a]

The Derfflinger class was a class of three battlecruisers (German: Schlachtkreuzer) of the Imperial German Navy. The ships were ordered for the 1912–13 Naval Building Program of the German Imperial Navy as a reply to the Royal Navy's two new Lion-class battlecruisers that had been launched a few years earlier. The preceding Moltke class and the incrementally improved Seydlitz represented the end of the evolution of Germany's first generation of battlecruisers. The Derfflinger 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 Derfflinger class used a similar propulsion system, and as a result of the increased displacement were slightly slower.

The class comprised three ships: Derfflinger, Lützow, and Hindenburg. All three of the ships saw active service with the High Seas Fleet during World War I. Derfflinger 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. Lützow was commissioned in August 1915, and participated only in the raid on Yarmouth before being sunk at Jutland. Hindenburg was commissioned into the fleet in May 1917, and saw no major action. Derfflinger and Hindenburg 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.

The Derfflinger-class battlecruisers were a result of the fourth and final Naval Law, which was passed in 1912. Admiral Alfred von 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.^[1] The three dreadnoughts secured in the bill became Derfflinger, Lützow, and Hindenburg.^[2] Design work on the first two ships began in October 1910 and continued until June 1911; Hindenburg was built to a slightly modified design, which was created between May and October 1912.^[3]

When design work began, the navy department was asked to submit new requirements to fix deficiencies found in the preceding battlecruiser classes, which primarily covered propulsion systems and the main armament. Previous battlecruisers used a four shaft arrangement for their engines; reducing the number to three would allow the new ships to equip a diesel engine on the central shaft. This would substantially increase the cruising range, and would ease the transfer of fuel and reduce the number of crew needed to operate the ships' machinery. The navy department also argued for an increase in the main battery guns, from 28-centimeter (11 in) guns to 30.5 cm (12 in) weapons. This was because the latest British battleships had thicker main belt armor, up to 300 millimeters (12 in). Since the German battlecruisers were intended to fight in the line of battle, their armament needed to be sufficiently powerful to penetrate the armor of their British opponents. Weight increases were managed by reducing the number of guns, from 10 to 8—the increase in gun caliber added only 36 tons to the ships' displacement. Tirpitz argued against the increase in gun caliber, for he thought the 28 cm gun was powerful enough.^[4]

A new construction technique was employed to save weight. Previous battlecruisers were built with a combination of transverse and longitudinal steel frames; the Derfflinger-class ships dispensed with the transverse frames and used only the longitudinal ones. This enabled the ship to retain structural strength and a lower weight. As with all preceding capital ships, the outer hull spaces between the hull wall and the torpedo bulkhead were used for coal storage.^[5]

On 1 September 1910, the design board chose the 30.5 cm, to be mounted in four twin turrets on the centerline of the ship. The armor layout was kept the same as in Seydlitz. 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.^[4]

Derfflinger and Lützow were 210 m (690 ft) long at the waterline and 210.40 m (690 ft 3 in) long overall. Hindenburg was slightly longer, at 212.50 m (697 ft 2 in) at the waterline and 212.80 m (698 ft 2 in) overall. All three ships had a beam of 29 m (95 ft 2 in), and a draft of between 9.20 m (30 ft 2 in) forward and 9.57 m (31 ft 5 in) aft. The first two ships were designed to displace 26,600 tonnes (26,200 long tons) with a standard load, and up to 31,200 tonnes (30,700 long tons) at combat weight. Hindenburg displaced slightly more, at 26,947 tonnes (26,521 long tons) standard and 31,500 tonnes (31,000 long tons) fully laden. The ships' hulls were constructed from longitudinal steel frames, over which the outer hull plates were riveted. Derfflinger's hull contained 16 watertight compartments, though Lützow and Hindenburg had an additional seventeenth compartment. All three ships had a double bottom that ran for 65% of the length of the hull.^[3] This was a decrease from preceding German battlecruisers, which had a double bottom for at least 75% of the hull.^[6]

The ships were regarded as excellent sea boats by the German navy.^[7] The Derfflinger-class ships were described as having had gentle motion, though they were "wet" at the casemate deck. 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 Derfflinger.^[b] The three ships had a metacentric height of 2.60 m (8 ft 6 in). 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 Derfflingers carried smaller craft, including one picket boat, three barges, two launches, two yawls, and two dinghies.^[7]

By the time construction work on Derfflinger began, it was determined that the diesel engine was not ready for use. Instead, the plan to use a three-shaft system was abandoned and the ships reverted to the standard four-shaft arrangement.^[4] Each of the three ships was equipped with two sets of marine-type turbines; each set drove a pair of 3-bladed screws that were 3.90 m (12 ft 10 in) in diameter on Derfflinger and Lützow and 4 m (13 ft 1 in) in diameter on Hindenburg.^[7] Each set consisted of a high- and low-pressure turbine—the high-pressure machines drove the outer shafts while the low-pressure turbines turned the inner pair.^[9] Steam was supplied to the turbines from 14 coal-fired marine-type double boilers and eight oil-fired marine-type double-ended boilers. Each ship was equipped with a pair of turbo-electric generators and a pair of diesel-electric generators that provided a total of 1,660 kilowatts at 220 volts. Each ship was equipped with two rudders.^[7]

The engines for first two ships were designed to provide 62,138 shaft horsepower (46,336 kW), at 280 revolutions per minute. This would have given the two ships a top speed of 26.5 knots (49.1 km/h; 30.5 mph). During trials, Derfflinger's engines achieved 75,586 shp (56,364 kW), but a top speed of 25.5 knots (47.2 km/h; 29.3 mph). Lützow's engines reached 79,880 shp (59,570 kW) and a top speed of 26.4 knots (48.9 km/h; 30.4 mph). Hindenburg's power plant was rated at 71,015 shp (52,956 kW) at 290 rpm, for a top speed of 27 knots (50 km/h; 31 mph). On trials she reached 94,467 shp (70,444 kW) and 26.6 knots (49.3 km/h; 30.6 mph). Derfflinger could carry 3,500 t (3,400 long tons) of coal and 1,000 t (980 long tons) of oil; at a cruising speed of 14 knots (26 km/h; 16 mph), she had a range of 5,600 nautical miles (10,400 km; 6,400 mi). Lützow carried 3,700 t (3,600 long tons) of coal and 1,000 tons of oil, though she had no advantage in range over her sister Derfflinger. Hindenburg also stored 3,700 tons of coal, as well as 1,200 t (1,200 long tons) of oil; her range at 14 knots was rated at 6,100 nautical miles (11,300 km; 7,000 mi).^[3]

The Derfflinger-class ships were armed with eight 30.5 cm (12 in) SK L/50 guns^[c] in four twin gun turrets, two forward of the main superstructure in a superfiring pair and two to the rear of the ship, in a similar arrangement. The guns were housed in Drh.L C/1912 mounts on the first two ships, and in Drh.L C/1913 mounts on Hindenburg. The turrets were trained with electric motors, while the guns were elevated hydraulically, up to 13.5 degrees. The guns fired 405.5-kilogram (894 lb) armor-piercing shells at a muzzle velocity of 855 meters per second (2,805 ft/s). At 13.5 degrees, the shells could hit targets out to 18,000 m (20,000 yd). The turrets were modified in 1916 to increase the elevation maximum to 16 degrees. This correspondingly increased the range to 20,400 m (22,300 yd). The ships carried 720 shells, or 90 per gun; each gun was supplied with 65 armor-piercing (AP) shells and 25 semi-AP shells for use against targets with less armor protection.^[11] The 30.5 cm gun had a rate of fire of between 2–3 shells per minute, and was expected to fire 200 shells before replacement was necessary. The guns were also capable of firing 405.9 kg (894.8 lb) high explosive shells. The shells were loaded with two RP C/12 propellant charges: a main charge in a brass cartridge that weighed 91 kg (201 lb) and a fore charge in a silk bag that weighed 34.5 kg (76 lb).^[12] The propellant magazines were located underneath the shell rooms for the two forward turrets as well as the rear superfiring turret; the arrangement was reversed for the rearmost turret.^[11]

The ships were designed to carry a secondary armament of fourteen 15 cm (5.9 in) SK L/45 guns, mounted in casemates along the superstructure. Because Derfflinger had to be fitted with anti-roll tanks, two of the casemated guns had to be removed, to allow enough room in the hull. Lützow and Hindenburg were equipped with the designed number of guns. Each gun was supplied with 160 rounds, and had a maximum range of 13,500 m (14,800 yd), though this was later extended to 16,800 m (18,400 yd).^[11] The guns had a sustained rate of fire of five to seven 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.^[13]

The three ships carried a variety of 8.8 cm (3.5 in) SK L/45 guns in several configurations. The Derfflinger-class ships were initially equipped with eight of these weapons, all in single mounts; four were placed in the forward superstructure and four in the aft superstructure. The ships also carried four 8.8 cm Flak L/45 anti-aircraft guns, which were emplaced around the forward funnel, with the exception of Lützow, which carried the Flak guns around the rear funnel. After 1916, the four 8.8 cm guns in the forward superstructure were removed.^[11] 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 (30,019 ft 8 in) at 70 degrees.^[14]

The ships were also armed with submerged torpedo tubes in their hulls. Derfflinger was equipped with four 50 cm tubes; the later ships were armed with more powerful 60 cm weapons.^[11] The tubes were arranged with one in the bow, one in the stern, and two on the broadside.^[7] Derfflinger's 50 cm torpedoes were the G7 type, 7.02 m (276 in) long and armed with a 195 kg (430 lb) Hexanite warhead. The torpedo had a range of 4,000 m (4,370 yd) when set at a speed of 37 knots, and up to 9,300 m (10,170 yd) at 27 knots. The 60 cm 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).^[15]

The Derfflinger-class ships were protected with Krupp cemented steel armor, as was the standard for German warships of the period. They had an armor belt that was 300 mm (12 in) thick in the central citadel of the ship, where the most important parts of the ship were. This included the ammunition magazines and the machinery spaces. The belt was reduced in less critical areas, to 120 mm (4.7 in) forward and 100 mm (3.9 in) aft. The belt tapered down to 30 mm (1.2 in) at the bow, though the stern was not protected by armor at all. A 45 mm (1.8 in) 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 (3.1 in) in the sections that covered the more critical areas of the ship.^[3]

The forward conning tower was protected with heavy armor: the sides were 300 mm thick and the roof was 130 mm (5.1 in) thick. The rear conning tower was less well armored; its sides were only 200 mm (7.9 in) thick and the roof was covered with 50 mm (2 in) of armor plate. The main battery gun turrets were also heavily armored: the turret sides were 270 mm (11 in) thick and the roofs were 110 mm (4.3 in) thick. On Hindenburg, the thickness of the turret roofs was increased to 150 mm (5.9 in). The 15 cm guns had 150 mm-worth of armor plating in the casemates; the guns themselves had 70 mm (2.8 in) thick shields to protect their crews from shell splinters.^[3]

Of the three ships in its class, only Derfflinger was ordered as an addition to the fleet, under the provisional name "K". The other two ships were to intended to replace obsolete vessels; Lützow was ordered as Ersatz Kaiserin Augusta for the elderly protected cruiser Kaiserin Augusta and the contract for Hindenburg was issued under the provisional name Ersatz Hertha, to replace the protected cruiser Hertha.^[3]

Derfflinger was constructed at Blohm & Voss in Hamburg under construction number 213. She was the least expensive of the three ships, at a cost of 56 million gold marks.^[7] The ship was ready to be launched on 14 June 1913, but during the ceremony, one of the wooden sledges upon which the hull rested became jammed. It took until 12 July for her to enter the water.^[16] She was commissioned into the High Seas Fleet on 1 September 1914, shortly after the outbreak of World War I. Lützow was built at the Schichau dockyard in Danzig under construction number 885, at the cost of 58 million gold marks. The ship was launched on 29 November 1913, and after lengthy trials, commissioned on 8 August 1915. Hindenburg, the final member of the class, was built at the Imperial Dockyard in Wilhelmshaven, under construction number 34. The ship was built at a cost of 59 million gold marks, the most expensive of the three vessels. She was launched on 1 August 1915 and commissioned on 10 May 1917.^[17]

Named after Georg von Derfflinger, a German field marshal during the Thirty Years' War, Derfflinger was commissioned on 1 September 1914. A dockyard crew transferred the ship from Hamburg to Kiel, via the Skagen. The ship was assigned to the I Scouting Group at the end of October. Damage to the ship's turbines sustained during trials prevented the ship from seeing active service until 16 November. On 15 December, the ship took part in the raid on Scarborough, Hartlepool and Whitby. She was also present during the battle of Dogger Bank on 24 January 1915. The ship was hit once by a 13.5-inch shell from one of the British battlecruisers; in response, she heavily damaged HMS Lion. Repair work was completed by 16 February, but Derfflinger's starboard turbine was accidentally damaged on 28 June, and the ship was again in the dockyard until August. On 24 April 1916, Derfflinger took part in the bombardment of Yarmouth.^[16]

On 31 May, Derfflinger was heavily engaged during the Battle of Jutland, as the second ship in the German battlecruiser line. She sustained 21 major hits during the battle, but dealt considerable damage to the British battlecruiser force as well. At 16:26, HMS Queen Mary sank after a magazine explosion that tore the ship apart; she had been targeted with a hail of heavy-caliber gunfire from Derfflinger and Seydlitz. Two hours later, at 18:30, HMS Invincible suffered a similar fate, though Derfflinger was assisted by her sister Lützow. During the engagement, Derfflinger had both of her rear turrets knocked out by British gunfire. Her crew suffered 157 men killed and 26 wounded, which was the highest casualty figure for any German ship not sunk. The resilience of the vessel earned her the nickname "Iron Dog" from her British adversaries.^[16] Repair work lasted until 15 October, during which the ship had her pole mast removed and replaced with a tripod mast. The ship conducted training operations until November, at which point she returned to active duty with the fleet.^[18]

Following the German capitulation in November 1918, Derfflinger was interned with a significant portion of the High Seas Fleet in Scapa Flow. On 21 June 1919, with the guard ships of the Royal Navy out on maneuvers, Rear Admiral Ludwig von Reuter ordered that the fleet be scuttled.^[d] The resulting scuttling of the German fleet saw some 66 vessels of various types sunk.^[20] Among those was Derfflinger, which sank at 14:45. The ship was raised in 1939 to be broken up for scrap metal, but the outbreak of World War II intervened. The ship, which remained capsized, was anchored off the island of Risa until 1946, at which point she was sent to Faslane Port, where she was broken up. The ship's bell was delivered to the German Federal Navy on 30 August 1965.^[7]

Lützow was named after Ludwig Adolf Wilhelm von Lützow, a Prussian lieutenant-general who fought during the Napoleonic Wars. The ship was commissioned on 8 August 1915, and then underwent trials. On 25 October, while still running sea trials, Lützow's port low pressure turbine was severely damaged. She was sent to Kiel for repairs, which lasted until late January 1916. The ship went on additional trials that lasted until 19 February. Lützow was by then fully operational, and assigned to I Scouting Group on 20 March 1916. She took part in two fleet advances, on 25 March and 21–22 April, without any major incidents. The following day, on 23 April, Lützow, along with her sister Derfflinger and the battlecruisers Seydlitz, Moltke, and Von der Tann, bombarded Yarmouth. While en route to the target, Vice Admiral Franz von Hipper's flagship Seydlitz was heavily damaged by mines. As a result, Lützow was transferred to the role of squadron flagship. During the operation, the German battlecruisers encountered British light forces, and a running battle ensued. Lützow engaged the light cruiser HMS Conquest and hit her several times.^[21]

At the Battle of Jutland, she was the first ship in the German line, and Hipper's flagship, and drew fire from the British battlecruisers which included hits below her waterline. Shortly after the start of the battlecruiser action, Lützow hit her opponent Lion several times; one hit knocked out Lion's "Q" turret, and the resulting magazine fire nearly destroyed the ship.^[e] Shortly after 19:00, the armored cruisers Defence and Warrior inadvertently ran into the German line; Lützow opened fire immediately, followed by several German dreadnoughts. In a hail of shells, Defence's ammunition magazines detonated and the ship was sunk.^[22] At around the same time, the fresh battlecruisers of the 3rd Battlecruiser Squadron engaged their German opposites. Between 19:26 and 19:34, Lützow sustained four 12-inch shell hits in her bow from the British battlecruisers; these eventually proved to be fatal. Despite this, at 19:30, the combined fire of Lützow and her sister Derfflinger destroyed the battlecruiser Invincible. By 20:15, Lützow had been hit five more times, including hits on her two forward turrets.^[23]

By 22:15, Lützow had shipped nearly 2,400 tons of water, and the ship was dangerously down by the bows. After midnight, attempts were made to steer the ship in reverse. This failed when the bow became submerged enough to bring the stern out of the water; by 02:20, the screws and both rudders were coming out of the water and the ship was no longer able to steer. The order to abandon ship was given, and at 02:47, Lützow was sunk by the torpedo boat G38. The ship was lost because the flooding in the bow could not be controlled; the forward pump system failed and the central system could not keep up with the rising water.^[23] The crew was picked up by four torpedo boats that had been escorting the crippled battlecruiser; during the battle the ship suffered 116 men killed.^[24]

Hindenburg was the last battlecruiser completed for the Imperial German Navy, and as such had a very short career. She was commissioned 10 May 1917, and was fully operational by 20 October 1917, too late to see any major action in World War I. On 17 November Hindenburg and Moltke, along with the light cruisers of II Scouting Group, were acting as distant support for German minesweepers off the German coast when they were attacked by British battlecruisers. The raid was brief; by the time Hindenburg and Moltke arrived on the scene, the British ships had broken off the attack and withdrawn. Six days later, Hindenburg replaced Seydlitz as flagship of I Scouting Group.^[f] On 23 April 1918, the ship took part in an abortive fleet advance into the North Sea that attempted to intercept an Allied convoy. Moltke sustained mechanical damage while en route, and as a result, Vice Admiral Hipper decided to cancel the operation. On 11 August, Hipper was promoted to Admiral and given command of the entire High Seas Fleet. Rear Admiral Ludwig von Reuter replaced Hipper as the commander of I Scouting Group; he raised his flag on Hindenburg the following day.^[24]

Hindenburg was interned at Scapa Flow, along with her sister Derfflinger and the rest of the German battlecruisers. She was scuttled on 21 June 1919, and sank at 17:00. Several unsuccessful attempts to raise her were made; on 23 July 1930 the ship was finally raised. From 1930 to 1932 she was scrapped at Rosyth. Her bell was presented to the German Federal Navy on 28 May 1959.^[7]

Wikimedia Commons has media related to Derfflinger class battlecruisers.

• Bennett, Geoffrey (2005). Naval Battles of the First World War. Barnsley: Pen & Sword Military Classics. ISBN 978-1-84415-300-8.
• Grießmer, Axel (1999). Die Linienschiffe der Kaiserlichen Marine: 1906–1918; Konstruktionen zwischen Rüstungskonkurrenz und Flottengesetz [The Battleships of the Imperial Navy: 1906–1918; Constructions between Arms Competition and Fleet Laws] (in German). Bonn: Bernard & Graefe Verlag. ISBN 978-3-7637-5985-9.
• Gröner, Erich (1990). German Warships: 1815–1945. Vol. I: Major Surface Vessels. Annapolis: Naval Institute Press. ISBN 978-0-87021-790-6.
• Herwig, Holger (1998) [1980]. "Luxury" Fleet: The Imperial German Navy 1888–1918. Amherst: Humanity Books. ISBN 978-1-57392-286-9.
• Staff, Gary (2006). German Battlecruisers: 1914–1918. Oxford: Osprey Books. ISBN 978-1-84603-009-3.
• Tarrant, V. E. (2001) [1995]. Jutland: The German Perspective. London: Cassell Military Paperbacks. ISBN 978-0-304-35848-9.

• DiGiulian, Tony (28 December 2008). "Germany 30.5 cm/50 (12") SK L/50". NavWeaps.com. Retrieved 24 July 2009.
• DiGiulian, Tony (6 July 2007). "German 15 cm/45 (5.9") SK L/45". NavWeaps.com. Retrieved 24 July 2009.
• DiGiulian, Tony (16 April 2009). "German 8.8 cm/45 (3.46") SK L/45, 8.8 cm/45 (3.46") Tbts KL/45, 8.8 cm/45 (3.46") Flak L/45". NavWeaps.com. Retrieved 24 July 2009.
• DiGiulian, Tony (21 April 2007). "German Torpedoes Pre-World War II". NavWeaps.com. Retrieved 24 July 2009.

• Breyer, Siegfried (1997). Die Kaiserliche Marine und ihre Großen Kreuzer [The Imperial Navy and its Large Cruisers] (in German). Wölfersheim: Podzun-Pallas Verlag. ISBN 3-7909-0603-4.
• Campbell, N. J. M. (1978). Battle Cruisers. Warship Special. Vol. 1. Greenwich: Conway Maritime Press. ISBN 978-0-85177-130-4.
• Dodson, Aidan (2016). The Kaiser's Battlefleet: German Capital Ships 1871–1918. Barnsley: Seaforth Publishing. ISBN 978-1-84832-229-5.
• Dodson, Aidan; Cant, Serena (2020). Spoils of War: The Fate of Enemy Fleets after the Two World Wars. Barnsley: Seaforth Publishing. ISBN 978-1-5267-4198-1.
• Staff, Gary (2014). German Battlecruisers of World War One: Their Design, Construction and Operations. Barnsley: Seaforth Publishing. ISBN 978-1-84832-213-4.