Orion-class battleship

The Orion-class battleships were four super-dreadnought battleships — the first ships of that type — of the Royal Navy. The lead ship, HMS Orion (1910), was launched in 1910. They were the first Royal Navy dreadnoughts to have all their main guns in the centreline; the U.S. Navy's first dreadnoughts, the, had pioneered this advanced feature. The Orions were quite distinct from the later classes of 13.5-inch gun super-dreadnoughts (the s and s) in that the mainmast was placed behind the fore-funnel. This arrangement was common in early Royal Navy dreadnoughts but created major problems for the gunnery direction team in the spotting top.

Design and development
Previous British dreadnoughts had been built very much with an eye on cost. By 1909, the escalating Anglo-German naval arms race had released greatly increased resources from the British treasury. These ships were much bigger than the preceding and cost almost £1.9 million each  to construct.

Armament
The move to the 13.5 in gun came out of necessity. The final iteration of the 12 in, the high velocity 50 calibre long Mark XI, had been unsuccessful. It lost some of its accuracy and was subject to considerable bore erosion that limited its useful life to about 80 discharges. A lower velocity weapon was indicated, and this was realized in the 13.5-inch, 45 calibres long, and with a much heavier projectile. The projectile used was 1250 lb or 1400 lb against 850 lb. The shorter range of the low-velocity gun was compensated by increasing the maximum elevation from 15 to 20 degrees. The 13.5-inch was considered a successful design, although its effectiveness was compromised by poor shell design until availability of the "Green Boy" shells in 1918.

The adoption of the all-centreline armament was also borne of necessity. The previous and es had already adopted a superfiring pair of turrets aft in an effort to save deck space, and competing designs in the U.S. and elsewhere had led the way in the all-centreline arrangement. From a combat efficiency standpoint the staggered turret configuration of the Colossuses and Neptunes complicated internal arrangements and was generally not considered a success. Unfortunately, the retention of outdated sighting hoods meant the Orions were not able to fire the superimposed turrets over the deck turrets for fear that the blast would injure crews in the lower turrets. Also, the design's relatively high centre of gravity gave the Orions a pronounced roll in rough seas. Both these defects were eventually cured and the improvements included in subsequent classes of British dreadnoughts.

Armour
The armour belt was increased to 12 in in view of the general increase in gun calibre of potential adversaries. It is typical of British designs where armour thickness lagged behind their carried gun size, this being the opposite design driver of German ships in which armour thickness was usually greater than the calibre of the guns they carried. It is also of interest to note adequacy of ship armour was still being judged by belt thickness, while deck thickness was a secondary consideration. This became more critical as battle ranges extended beyond approximately 12,000 yards (11 km) as the trajectory of the incoming shells became increasingly vertical. Practice ranges prior to the First World War were rarely greater than 5000 yd at which the trajectory was nearly flat. By the time the initial actions were being fought the ranges exceeded 18000 yd, where on occasions all capital ships on both sides were vulnerable to "plunging" fire. (German ships were somewhat less vulnerable by virtue of having very high belts, which kept shells away from the armour decks, and because British shells were notoriously weak at penetrating armour at an oblique angle).

History
All four were present at the Battle of Jutland of 1916 in World War I, but took no damage. They had a relatively short career, all being decommissioned in 1921, due to the Washington Naval Treaty. Orion and Conqueror were scrapped in 1922. Monarch served as a target, surviving a full day of shelling and bombing on 20 January 1925 before being sunk by fire from HMS Revenge (06). Thunderer served longest, acting as a training ship from 1922 until she, too, was sold for scrap in December 1926.

Ships of the class

 * HMS Conqueror (1911)
 * HMS Monarch (1911)
 * HMS Orion (1910)
 * HMS Thunderer (1911)