Iron Duke - class battleship The " Iron Duke " class was a group of four dreadnought battleship s built for the British Royal Navy before the First World War . The class comprised four ships : , , , and . Launched from October 1912 to November 1913 , this was the third class of Royal Navy super - dreadnoughts . The ships were essentially repeats of the battleships ; they retained the same ten 13 . 5 inch ( 34 . 3 cm ) guns in five twin gun turret s on the centreline . However , the " Iron Duke " s had improved armour and a more powerful secondary armament of 6 - inch weapons instead of the 4 - inch mounted on the earlier ships . The four ships were the most advanced battleships in the Royal Navy at the outbreak of the First World War , though they were soon surpassed by the five ships of the . They all saw extensive service during the war with the Grand Fleet , where " Iron Duke " acted as the flagship for the fleet commander , Admiral John Jellicoe . Three of the ships , " Iron Duke " , " Benbow " , and " Marlborough " , were present at the Battle of Jutland ; the " Emperor of India " missed the battle by being in dock for periodic refit . The four " Iron Duke " - class battleships saw limited active duty following the end of the war ; they were all demilitarised under the terms of the Washington Naval Treaty signed in 1922 . " Iron Duke " was reduced to a training and depot ship and lasted in that role until 1946 when she was scrapped . " Benbow " was scrapped in 1931 and " Marlborough " followed in 1932 . " Emperor of India " was sunk as a gunnery target in 1931 . Design . General characteristics . The " Iron Duke " - class ships were 622 feet 9 inches ( 189 . 9 metres ) long overall , and had a beam of 90 ft ( 27 . 4 m ) and a draught of 29 ft ( 8 . 8 m ) . This was an increase of 25 ft ( 7 . 7 m ) in length and 1 ft ( . 3 m ) in width over the preceding " King George V " - class ships . The " Iron Duke " s displaced 25 , 000 long tons ( 25 , 400 tonnes ) . This was some 2 , 000 tons ( 2 , 032 tonnes ) heavier than the preceding " King George V " s , and was primarily due to the increase in calibre of the secondary battery . The ships were powered by four - shaft Parsons turbines . Steam was provided to the turbines by 18 Babcock & Wilcox or Yarrow boilers . The engines were rated at 29 , 000 shaft horsepower and delivered a top speed of . " Iron Duke " and her sisters had a fuel storage capacity of of coal and of oil . This enabled a maximum range of at a cruising speed of . Armament . Primary battery . The " Iron Duke " - class ships mounted a main battery of ten 13 . 5 inch ( 34 . 3 cm ) Mk V ( H ) guns in five twin gun turret s , all mounted on the centreline . Two turrets were placed in a superfiring pair forward ( " A " and " B " turrets ) , one turret amidships — the " Q " turret — directly after the two funnels , and two in a superfiring pair aft of the rear superstructure ( " X " and " Y " turrets ) . The gun houses used were Mk II turrets that weighed 600 tons ( 610 tonnes ) and allowed for depression to −5° and elevation to 20° . Despite this , the range dials on the gunsights at the time of construction were graduated to 15 degrees ; super - elevating cams and prisms to allow the full elevation of the guns to be used were issued some time after the Battle of Jutland . The forward and aft gun turrets could train 150° in either direction from the centreline , while the " Q " had a much more limited range . It could engage targets on an arc from between 30° to 150° from the centerline on either beam of the ship . The guns had a rate of fire of between 1 . 5 – 2 rounds per minute . The Mk V " Heavy " gun fired a variety of shells , including high explosive and armour - piercing rounds ; they all weighed 1 , 400 lb ( 635 kg ) . The guns were loaded with MD45 propellant charges that weighed 297 lb ( 135 kg ) ; these were stored in silk bags . This provided a muzzle velocity of 2 , 491 fps ( 759 meters per second ) . At maximum elevation of 20° , the guns had a range of 23 , 740 yards ( 21 , 710 m ) , though at the maximum effective range of 15° , the range was somewhat shorter , at approximately 20 , 000 yd ( 18 , 290 m ) . At a range of 10 , 000 yd ( 9 , 144 m ) , the gun could penetrate up to 12 . 5 in ( 318 mm ) of Krupp cemented steel armour , the type used on contemporary German dreadnoughts . Secondary battery . The secondary battery consisted of twelve 6 - inch ( 15 . 2 cm ) Mk VII guns mounted in casemate s in the hull around the forward superstructure . These guns were chosen because the 4 - inch ( 10 . 2 cm ) guns on earlier battleships were deemed to be too weak and have too short a range to effectively combat torpedo boats with newer , more powerful torpedoes . Admiral Jackie Fisher had opposed the idea of increasing the secondary battery , though he retired from the post of First Sea Lord in 1910 . As a result , the " Iron Duke " s , which were designed in 1911 , received the larger 6 inch gun . These guns fired 100 lb ( 45 . 4 kg ) shells at a rate of between 5 – 7 per minute . The shells were fired with a muzzle velocity of 2 , 775 fps ( 846 mps ) , though the guns were capable of higher velocities . It was reduced in order to standardize the performance of all the 6 inch guns in Royal Navy service , which would simplify range calculations for guns of the calibre . The guns could elevate to 20° , which enabled a maximum range of 15 , 800 yd ( 14 , 450 m ) . There were some significant problems with the casemate guns early on , however . They were equipped with hinged plates that were designed to close off the casemate opening in heavy seas . The plates were easily washed away , though , and without them , water easily entered the ship and caused significant flooding . This problem was compounded by the fact that they had been mounted too low in the hull , which subjected them to heavier pounding from rough seas . The problem was eventually corrected by the addition of dwarf bulkheads in the gun houses and rubber seals to the hinged plates . Other armament . " Iron Duke " was the first British battleship to be mounted with anti - aircraft weaponry . In 1914 , two 3 in ( 7 . 62 cm ) QF guns were fitted to the aft superstructure , primarily to defend against German airships . The guns fired between 12 – 14 rounds per minute , and were expected to fire approximately 1 , 250 shells before replacement or repair was necessary . The shells fired were 12 . 5 lb ( 5 . 67 kg ) with a high - explosive warhead . They were manually operated , and had a maximum effective ceiling of 23 , 500 ft ( 7 , 160 m ) . As was customary for capital ships of the period , the " Iron Duke " - class ships were equipped with submerged torpedo tubes . The ships carried four 21 in ( 53 . 3 cm ) tubes , two on each beam . These launched Mk II torpedoes that carried a 515 lb ( 234 kg ) TNT warhead . They had could be set at two speed settings : and . At 31 knots , the range was 10 , 750 yd ( 9 , 830 m ) , though at 45 kn the range was considerably reduced , to 4 , 500 yd ( 4 , 110 m ) . Armour . The " Iron Duke " - class battleships had an armour belt that was thick in the central area of the ship , where the ammunition magazines , machinery spaces , and other vital parts of the ship were located . The belt tapered down to towards the bow and stern . The barbette s that contained the main gun turrets were on the sides and on the rear , where shells were less likely to hit . The turrets themselves were thick on the sides . The ships ' armoured deck was between 25 – 65 mm ( 1 – 2 . 5 in ) thick . After the battle of Jutland in May 1916 , some 820 tonnes of armour was added to the ships , primarily to thicken the deck around the main battery turrets , as well as to increase the bulkheads in the ammunition magazines . Construction . " Iron Duke " was laid down on 12 January 1912 in the Portsmouth Dockyard . She was launched exactly 10 months later , on 12 October 1912 ; fitting out work commenced thereafter , and was finished by March 1914 . She was then commissioned into the British Home Fleet , as the flagship of Admiral George Callaghan . " Marlborough " was the second ship of the class to be built . She followed " Iron Duke " by nearly two weeks ; " Marlborough " was laid down at the Devonport Dockyard on 25 January 1912 and launched on 24 October 1912 . Fitting out work proceeded somewhat slower on the ship , which wasn ' t finished until June 1914 . " Benbow " was laid down at Beardmore on 30 May 1912 , more than 5 months after her older sisters . She was launched on 12 November 1913 and completed by October 1914 . " Emperor of India " , the last of the four battleships , was originally ordered under the name " Delhi " . She was laid down at Vickers the day after " Benbow " , on 31 May 1912 . She was launched on 27 November 1913 , and completed by November 1914 . Service . " Iron Duke " . Upon commissioning , was assigned to the Home Fleet as the fleet flagship . After the outbreak of the First World War , the Royal Navy was reorganized ; the Home Fleet and the Atlantic Fleet were combined to form the Grand Fleet ; " Iron Duke " retained her position as fleet flagship , under John Jellicoe . The ship took part in all of the major fleet actions , though only one of them ended in combat — the sortie on 31 May that resulted in the Battle of Jutland . At Jutland , " Iron Duke " was assigned to the 3rd Division of the 4th Battle Squadron , and was stationed in the centre of the British line . Following the end of the war , " Iron Duke " was transferred to the Mediterranean Fleet . During 1919 – 20 , the ship operated in the Black Sea in support of the White Russians during the Russian Civil War . The Washington Naval Treaty of 1922 mandated that " Iron Duke " be removed from the active roster . However , she remained with the fleet for a short time , having been transferred to the Atlantic Fleet in 1926 . This duty assignment lasted 3 years , after which she was removed from active service . She was demilitarised , to be used as a training ship . Two of her gun turrets and a good deal of her armour were removed , and her speed was reduced to through the removal of some of her boilers . She was later used as a depot ship in Scapa Flow , starting in 1939 . After the outbreak of the Second World War that year , her remaining guns were removed to be used in shore defences . " Luftwaffe " bombers attacked her on 17 October 1939 ; while they scored no direct hits , several near misses caused significant damage . After repairs were effected , the ship resumed her duties as a depot vessel until the end of the war . She was finally sold for scrapping in 1946 . " Marlborough " . was the most heavily engaged ship of the class during the battle of Jutland ; she fired a total of 162 heavy - calibre shells , out of a total of 292 for the entire class . She was assigned to the 6th Division of the 1st Battle Squadron , towards the rear of the British line . She served as the flagship of Vice Admiral Cecil Burney . During the battle , she was hit by a torpedo amidships ; the torpedo tore a hole that was 21 m by 6 m ( 70 ft by 20 ft ) . Despite the damage , she was able to keep her position in the line , though her speed was reduced to . " Marlborough " continued to fire her main guns until the list increased to the point that prevented her guns from being effectively employed . The ship eventually withdrew to the Humber , where she undertook 3 months of repairs . Post - war , " Marlborough " joined " Iron Duke " in the Mediterranean , where she remained until 1926 . She was then transferred to the Atlantic Fleet ; her tour of duty there lasted until 1929 , at which point she was withdrawn from active duty . The ship was sold for scrapping in 1932 . " Benbow " . Like her sisters , was assigned to the Grand Fleet for the duration of the First World War . She was assigned to the 4th Battle Squadron on 10 December 1914 . " Benbow " was the flagship of Admiral Doveton Sturdee , the commander of the 4th Division of the 4th Battle Squadron , during the battle of Jutland . The 4th Division was directly ahead of the 3rd Division , where Admiral Jellicoe commanded the fleet from " Benbow " s sister " Iron Duke " . Throughout the battle the ship remained undamaged . Like " Iron Duke " and " Marlborough " , " Benbow " was transferred to the Mediterranean in 1919 , and she provided artillery support to White Russian forces in the Black Sea . She followed " Marlborough " to the Atlantic Fleet in 1926 ; she too was stricken in 1929 and sold for scrap . " Emperor of India " . was also assigned to the 4th Battle Squadron , in December 1914 . She missed Jutland because she was in dock for a periodic refit . After the end of the war , she was transferred to the Mediterranean along with the other three ships of the class . " Emperor of India " returned to England in 1922 for a refit , after which she resumed her duties in the Mediterranean . She likewise joined the Atlantic Fleet in 1926 , alongside her sisters , and stricken in 1929 . Instead of being scrapped , however , she was used as a gunnery target , and sunk in 1931 . She was raised shortly thereafter and sold to ship breakers on 6 February 1932 .