Class overview
Name:	Orion
Preceded by:	Colossus class
Succeeded by:	King George V class
In commission:	1912-1922
Completed:	4
General characteristics
Type:	Super-dreadnought battleship
Displacement:	22,000 tons normal 25,870 tons max
Length:	581 ft (177.1 m)
Beam:	88 ft (26.8 m)
Draught:	24 ft (7.3 m)
Propulsion:	Direct-drive[1] steam turbines, 18 boilers, 4 shafts: 27,000 hp (20 MW)
Speed:	21 knots (38.9 km/h)
Range:	6,730 nm at 10 knots (12,450 km at 18.5 km/h)
Complement:	750–1100
Armament:	10 × BL 13.5 inch /45 cal Mk V guns (5×2) 16 × BL 4 inch Mk VII guns (16×1) 3 × 21-inch (533 mm) torpedo tubes (submerged)
Armour:	Belt: 12 in (305 mm) Bulkheads: 10 in (254 mm) Decks: 4 in (102 mm) Turrets: 11 in (279 mm) Barbettes: 10 in (254 mm)

The Orion class battleships were four super-dreadnoughts — the first ships of that type — of the Royal Navy. The lead ship, Orion, 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 South Carolina class, had pioneered this advanced feature. The Orions were quite distinct from the later classes of 13.5" super-dreadnoughts (King George Vs and Iron Dukes) in that the fore-funnel was placed in front of the mainmast. 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.^{[citation needed]} By 1909, although war still seemed unlikely, the white-hot naval rivalry had loosened the purse strings. These ships were much bigger than the preceding Colossus class and cost almost £1.9 million each to construct.

  Armament

The move to the 13.5-inch (343 mm) gun came out of necessity. The final iteration of the 12-inch (305 mm), the high velocity 50 calibre Mark XI,^[2] 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 was realized in the 13.5-inch, of 45 calibres, and with a much heavier projectile. The projectile used was 1,250 lb (567 kg) or 1,400 lb (635 kg) against 850 lb (386 kg). 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.^[3]

The adoption of the all-centreline armament was also of necessity. The previous Colossus and Neptune classes 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. The great investment in displacement and cost of a 13.5-inch turret contra-indicated wing turrets, with their limited arcs of fire and therefore limited effectiveness. Finally, the staggered arrangement of the Colossuses and Neptune 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 wicked 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 inches (305 mm) in view of the general increase in gun calibre in potential adversaries. It is quite typical of British designs armour thickness lagged behind 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 (horizontal) thickness, rather than deck (vertical) thickness which became more critical as battle ranges extended beyond approximately 12,000 yards (11 km) as the trajectory of the incoming shells was more vertical than the design of the ships was intended to resist. Practice ranges prior to the war were rarely greater than 5,000 yd (4,600 m) at which the trajectory was nearly flat.^{[citation needed]} By the time that the initial actions were being fought at ranges exceeding 18,000 yd (16,500 m) on occasions all capital ships on both sides were vulnerable to "plunging" fire. (German ships were less vulnerable by virtue of having very deep 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. Thunderer served longest, acting as a training ship from 1922 until she, too, was sold for scrap in December 1926.

  Ships of the class

• Conqueror
• Monarch
• Orion
• Thunderer

  References

Battleships portal

  External Sources

Wikimedia Commons has media related to: Orion class battleship

• Dreadnought Project Technical material on the weaponry and fire control for the ships