Cochrane displaced as built and fully loaded, with a length of, a beam of and a draft of. She was powered by four-cylinder triple-expansion steam engines, driving two shafts, which developed a total of and gave a maximum speed of. The engines were powered by 19 Yarrow water-tube boilers and six cylindrical boilers. The ship carried a maximum of of coal and an additional of fuel oil that was sprayed on the coal to increase its burn rate. At full capacity, she could steam for at a speed of. Her main armament consisted of six BL Mark X guns in single Mk V turrets distributed in two centerline turrets and four turrets disposed in the corners about the funnels. Her secondary armament of four BL Mark II or Mark V guns in single Mk II turrets was carried amidships, between the wing 9.2-inch guns. Twenty-six Vickers QF 3 pounders were fitted, ten on turret roofs and eight each on the forward and aft superstructures. The last four ships of the cruisers had a secondary armament of turreted 7.5-inch guns rather than the guns in open barbettes of the first two ships; these latter four were sometimes referred to as the Warrior class. Because of the extra topweight of the turrets in comparison to their half-sisters their stability was reduced which made them very good seaboats and steady gun platforms.
Wartime modifications
A single Hotchkiss QF 6-pounderanti-aircraft gun on a high-angle Mark Ic mounting was mounted on the quarterdeck in 1915. It had a maximum depression of 8° and a maximum elevation of 60°. The gun fired a shell at a muzzle velocity of at a rate of fire of 20 rounds per minute. They had a maximum ceiling of, but an effective range of only. It was replaced by a QF 3 inch 20 cwt guns on a high-angle Mark II mount in 1916. This gun had a maximum depression of 10° and a maximum elevation of 90°. It fired a shell at a muzzle velocity of at a rate of 12–14 rounds per minute. It had a maximum effective ceiling of. A pair of Vickers QF 3 pounder on HA Mark III mountings were probably installed amidships during 1915–16. They could elevate to +80° and depress to -5°. This gun fired a shell at a muzzle velocity of at a rate of 25 rounds per minute. They had a maximum ceiling of, but an effective range of only. The gunson top of 'A' and 'Y' turrets were removed in 1915–16. The aftermost 3-pounder guns on the superstructure were removed during 1917 as well as the guns on top of the forward 9.2-inch wing turrets. This reduced her total to twenty 3-pounder guns, excluding the AA guns. Some of these guns were landed at Murmansk while she was based there. Seventeen 3-pounders were on board when she was lost in 1919, but it is unclear if that total includes the AA guns. Cochranes foremast was converted to a tripod mast to support the weight of a fire-control director in 1917, but the director was not actually fitted until August 1918.
Service
Cochrane was laid down on 24 March 1904 and launched on 28 May 1905 at Fairfield Shipbuilding and Engineering, Govan, Scotland. The ship was commissioned with a nucleus crew on 18 February 1907 and cost £1,193,121. She "joined the Nore Division of the Home Fleet on 6 March 1907 and shortly afterwards was brought into full commission for service with the 5th Cruiser Squadron. On 1 April 1909 she recommissioned for service with the 2nd Cruiser Squadron with which she remained until September 1917." She escorted the Royal Yacht Medina in 1911–12. Cochrane, accompanied by her sister and three other armoured cruisers were sent to reinforce the defences of the Shetland Islands on 2 August 1914, days before the start of the First World War. She, and her squadron, were assigned to the Grand Fleet for most of the First World War. She took part in the Battle of Jutland on 31 May-1 June 1916, along with the cruisers,, and under the command of Rear-Admiral Herbert Heath. However, the ship remained unengaged throughout the battle, and did not fire her 9.2 or 7.5-inch guns at all during the battle. Cochrane was transferred to the North America and West Indies station in November 1917, but rejoined the 2nd Cruiser Squadron early in 1918. She was based in Murmansk between March and September 1918 during the Allied intervention in the Russian Civil War. She ferried Soviet troops to Pechenga on 3 May to forestall an attempt by White Finns to seize the town. On 14 November 1918 she was stranded in the Mersey Estuary, while under the control of the pilot, and later broke in two, becoming a total loss. The wreck had been broken up in situ by June 1919.
