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The G3 battlecruisers were a design of battlecruiser planned for the Royal Navy after the First World War. The G3's would have been larger, faster and more heavily armed than any existing battleship and the battlecruiser aspect was more in the balance of speed and armament relative to the N3 battleship design considered at the same time.

They were the latest of several designs being considered. They were G from a series of battlecruiser designs working backwards from K and 3 for triple turrets. The battleship designs used the letters from L upwards. The first design had been L2, followed by M2 and N3.

The introduction of the Washington Naval Treaty, an arms limitation treaty intended to curtail an arms race between competing navies in the post-Great War period, led to the suspension of building in November 1921 and outright cancellation in February 1922.

Many of the aspects of their design made their way into the Nelson class battleships which are often viewed as cut-down G3's. The Nelsons received the designation O3, marking them as next in the design line from the N3 battleships although they used the G3's guns (which were already under construction) to comply with the Treaty.

Among the names speculated for the four ships planned were Invincible, Indomitable, Inflexible and Indefatigable^{[citation needed]} from the World War I battlecruisers, and for the N3 battleships under consideration at the same time St George, St Patrick, St Andrew and St David after the patron Saints of the four nations of the UK.

Contents 1 Design 2 Planned specification 3 References 4 See also

The G3 design took several novel ideas.

• concentration of the main battery forward of the funnels. This has been attributed to the idea that since British ships never ran away from a battle, they did not need to fire astern and could concentrate all guns on the enemy without turning side on. Actually to achieve the desired scale of armour protection it was necessary to reduce the length of the armoured part of the ship to a minimum. This led to the concentration of the turrets and associated magazines and hence the limited firing arcs and was repeated in the design of the French Dunkerque fast battleships and Richelieu battleships. As they each had only two turrets these were given as wide a separation as allowed by the other design constraints.

• complete armour protection for all important areas and none for the rest - described as 'the all or nothing system'.

• a tower bridge structure, which was designed to reduce draughts and be made secure against gas attack. The tower bridge was sited behind the first two gun turrets and in front of the third which consequently suffered from restricted firing arcs.

• dual purpose secondary armament - with the ability to fire at surface targets and to provide 'barrage fire' against (torpedo bomber) aircraft.

• a dedicated anti-aircraft battery with directed fire. Ships had anti-aircraft guns fitted before but were ineffective as the aiming was not controlled.

• a properly designed and tested anti-torpedo protection system.

• oxygen enriched torpedoes - Japanese naval observers learned of these after the Nelson class battleships were completed and their reports prompted the Japanese navy to develop their famous Long Lance torpedoes.

• Displacement: 48,400 tons
• Length: 862 ft 6 in
• Breadth: 106 ft
• Draft: 32 ft 6 in
• Armour
  • Belt: 14"
  • Barbettes: 14"
  • Deck 9" to 4.5"

• Armament:
  • Main: nine BL 16 inch /45 naval guns in 3 triple turrets
  • Secondary: sixteen 6 inch guns in 8 twin turrets
  • Anti-aircraft:
    • six QF 4.7 inch
    • four 10 barrel Pom-pom (40 mm) mountings
• Propulsion
  • 20 boilers in 9 boiler rooms
  • geared steam turbines 160,000 shp.
  • speed 31.5/32 knots

It is interesting to note that had the G3's been laid down, completed and met their design specifications as planned, the Royal Navy would have possessed from the late 20's onwards a class of warships more or less equivalent to the US Navy Iowa class designed twenty years later.

• Siegfried Breyer, Battleships and Battlecruisers 1905-1970 (Doubleday and Company; Garden City, New York, 1973) (originally published in German as Schlachtschiffe und Schlachtkreuzer 1905-1970, J.F. Lehmanns, Verlag, Munchen, 1970).

• Lexington class battle cruiser - a contemproary US design also cancelled by the Washington naval treaty

G3 battlecruiser

Four ships planned 1921 - none built.

List of battlecruisers of the Royal Navy