The St Vincent-class battleships were a group of three dreadnought battleships built for the Royal Navy in the first decade of the 20th century. The sister ships spent their entire careers assigned to the Home and Grand Fleets. Aside from participating in the Battle of Jutland in May 1916 and the inconclusive action of 19 August several months later, their service during the First World War generally consisted of routine patrols and training in the North Sea. was destroyed in 1917 by a magazine explosion with the near total loss of her crew. The remaining pair were obsolete by the end of the war in 1918, and spent their remaining time either in reserve or as training ships before being sold for scrap in the early 1920s.
Vanguards wreck was extensively salvaged before it was declared a war grave. Since 2002, it has been designated as a controlled site under the Protection of Military Remains Act 1986 and diving on the wreck is generally forbidden.
Background and description
The Admiralty's 1905 draft building plan called for four capital ships in the 1907–1908 Naval Programme, but the new Liberal government cut one of these ships in mid-1906 and postponed another to the 1908–1909 Naval Programme, pending the conclusion of the ongoing Hague Peace Convention. The failure of the Germans to agree to any sort of naval arms control caused the government to reinstate the third ship. The Admiralty took until 12 June 1907 to decide not to build one of them as a battlecruiser, in favour of a squadron of four homogeneous battleships. Three of these would be part of the St Vincent class, while the single battleship planned for the 1908–1909 Naval Programme was later authorised as .
thumb|left|Right elevation and plan of the first generation of British dreadnoughts from the 1912 edition of [[Brassey's Naval Annual]]
The design of the St Vincent class was derived from the preceding , with more powerful guns and a slight increase in size and armour. The ships had an overall length of , a beam of , and a normal draught of . They displaced at normal load and at deep load. In comparison to the Bellerophon class, the displacement of the St Vincents was increased by , the length by and the beam by ; their crews numbered about 755 officers and ratings upon completion and 835 during the war.
The St Vincent-class ships were powered by two sets of Parsons direct-drive steam turbines, each of which was housed in a separate engine room. The outer propeller shafts were coupled to the high-pressure turbines and these exhausted into low-pressure turbines which drove the inner shafts. Separate cruising turbines were provided for each shaft. The turbines used steam from eighteen water-tube boilers at a working pressure of . They were rated at and were intended to give the ships a maximum speed of . During their sea trials, the St Vincents handily exceeded their designed speed and horsepower, reaching from . They carried of coal and an additional of fuel oil that was sprayed on the coal to increase its burn rate. This gave them a range of at a cruising speed of .
Armament
thumb|Vanguards starboard aft side, showing her rear 12-inch gun turret and anti-[[torpedo net booms, around 1914]]
These ships were the first to carry the new 50-calibre breech-loading (BL) Mark XI gun, which was 5 calibres longer and had a muzzle velocity about higher than the 45-calibre Mark X gun used in the earlier dreadnoughts. They had a reputation for drooping at the muzzle, which was believed to have an adverse effect at long range, but testing at sea showed the muzzle droop to be within normal tolerances and the accuracy at long range to be satisfactory. The increased muzzle velocity of the Mark XI gun gave it a longer range over the Mark X gun as well as increasing the distance at which it could penetrate 12 inches of armour from using the same shell. The higher velocity reduced its service life by increasing the wear in the barrel.
The St Vincent class were equipped with ten Mark XI guns in five hydraulically powered twin-gun turrets, three along the centreline and the remaining two as wing turrets. The centreline turrets were named 'A', 'X' and 'Y' from front to rear, and the port and starboard wing turrets were 'P' and 'Q' respectively. The ships carried between 80 and 100 shells per gun.