The Never Built Battlecruisers of 1921: The G3, Amagi and Lexington Classes


Artists Depiction of G3 Battlecruiser 

As the First World War ended a new Naval Race was heating up. The United States had announced its intention during the war to build a navy second to none while Imperial Japan was making plans for a fleet that would give it superiority in the Western Pacific. The British, though still be far the largest naval power in the world were burdened by the massive costs of war and empire, but also seeking to maintain their naval dominance.

The ships known as battle cruisers were first built by the British Royal Navy as a compliment to the all big gun Dreadnought battleships. The Battle Cruiser concept was a ship of roughly the same size and firepower as a Battleship but sacrificing protection for greater speed, endurance and range.  and Japan joined in the Battle Cruiser race before and during the war. The United States had concentrated on Battleships.


HMS Invincible Blowing Up at Jutland 

During the war the weaknesses of the type were exposed during the Battle of Jutland where three British Battle Cruisers, the HMS Invincible, HMS Indefatigable and HMS Queen Mary blew up with the loss of most of their crews of the  3311 officers and sailors on the ships only 26 survived. The HMS Lion was almost lost in a similar manner but for the heroic actions of her crew. The British ships had glaring deficiencies in armor protection and the arrangement of their ammunition magazines and hoists which certainly contributed to their loss. Their German counterparts on the other hand proved much tougher and though all sustained heavy damage while engaging British Battleships and Battle Cruisers, only one the Lützow was lost. She absorbed over 30 hits from large caliber shells and only lost 128 crew members.


As the war progressed other Battle Cruisers were built, the British launched the HMS Repulse and HMS Renown and completed the HMS Hood shortly after the war was over. The Japanese built the four ship Kongo class from a British design. As the powers embarked on the next Naval Race planners and naval architects designed ships of massive firepower, better protection and higher range and speed. All would have been better classed as Fast Battleships.

The British designed and began construction on the G3 class in 1921, the Japanese the Amagi Class, and the United States the Lexington Class. However the construction and completion of these ships as Battle Cruisers was prevented by the Washington Naval Treaty.

invincible 490

The treaty was ratified in 1922 limited the United States and Great Britain to a maximum of 525,000 tons in their battle ship fleets and 125,000 tons in aircraft carriers.  The Japanese agreed to a limit of 315,000 tons and the French and Italians 175,000 tons each. Tonnage for battleships was limited to a maximum of 35,000 tons with a limitation on guns size to 16 inches.  Since the bulk of the ships planned or being built by the US and Japan exceeded those limits they would be effected more than the British whose post war shipbuilding program had not begun in earnest, in fact the G3 Class had just been approved for construction.

The G3 class would have comprised four ships and been similar to the N3 Class Battleships. They were very well balanced ships and would have mounted nine 16” guns in three turrets on a displacement of 49,200 tons and deep load of 54,774 tons. They had an all or nothing protection plan meaning that the armored belt was concentrated in vital areas around the armored citadel, conning tower, turrets and magazines and engineering spaces. Their armor belt would have ranged from 12-14 inches, deck armor from 3-8 inches, conning tower 8 inches, barbettes 11-14 inches, turrets 13-17 inches and bulkheads 10-12 inches. Their propulsion system of 20 small tube boilers powering 4 geared steam turbines connected to 4 propeller shafts would have produced 160,000 shp with a designed speed of 32 knots.

The four ships, none of which were named were ordered between October and November of 1921. Their construction was suspended on November 18th 1921 and they and the N3 Battleships were cancelled in February 1922 due to the limitations of the Washington Naval Treaty. Many concepts of their design were incorporated in the Nelson Class Battleships.


Amagi Class as Designed, Akagi as Completed (below) 


The four planned Japanese Amagi Class ships would have mounted ten 16” guns on a displacement of 47,000 tons at full load. Their propulsion system 19 Kampon boilers powering four Gihon turbines would have given them a maximum speed of 30 knots, They would have had less protection than the G3 ships being more of a traditional Battle Cruiser design. As a result of the Washington Naval Treaty the Japanese elected to convert two of the ships, the Amagi and Akagi to aircraft carriers. Amagi was destroyed on the ways during the great Tokyo earthquake and Akagi was completed as a carrier. The other two vessels were scrapped on the ways.


The United States Navy planned the six ship Lexington Class. These ships would have mounted eight 16” guns on a ship displacing 43,254 tons at full load. They would have had a maximum speed of 33 knots being powered by 16 boilers which drove 4 GE electric turbines producing 180,000 shp. It was a massive engineering plant and the class did not have as heavy armor protection as either the G3 or Amagi classes but were superior in speed as well as endurance. Upon ratification of the Washington Naval Treaty four of the six ships were cancelled and the remaining two, the Lexington and Saratoga competed as aircraft carriers.  Had any of the ships been completed as Battle Cruisers it is likely due to their speed that they would have operated primarily with the the carriers that the US Navy built during the 1930s.


One can only speculate what the navies of World War II would have looked like had the Washington and the subsequent London Naval Treaties not been ratified. One can also only imagine how the war at sea would have been different had the ships completed as carriers been completed as Battle Cruisers.

However that was not to be, of the planned 14 ships of these three classes only three were completed, all as aircraft carriers. Thus they are an interesting footnote in the annals of naval ship design and not much more.

Until tomorrow,


Padre Steve+


Filed under History, Military, Navy Ships, US Navy

4 responses to “The Never Built Battlecruisers of 1921: The G3, Amagi and Lexington Classes

  1. Some of the lead-in designs to the “final” Lexington plans border on the hysterically funny, or hysterically scary, depending on your point of view. One would’ve been for a ship OVER 1,000 feet in length, with 12 stacks and two full decks of boilers! Thankfully, had we ever built the Lexingtons as gun ships, they would have been somewhat better, as the British allowed us to look over the Hood’s plans after WW1.
    And while the British BCs were VERY under-armoured, some of the Jutland problem was caused by flash protection measures being ignored, such as stacking powder charges in the hoist rooms (not in the protected magazines), or leaving the scuttles (where the charges moved from magasine to hoist) wide open – to increase rate of fire. You do have to admire the German BCs, though, willing to sacrifice a little gum-power for armour. The 13.8″-gunned Mackensens, and especially the 15″-gunned Ersatz Yorcks would have been terrifyingly powerful ships, indeed! (And let me guess, they’re the next topic, right? Oops – sorry! 😦 )
    (Rats – I can’t find the site that has a whole bunch of “GrossKreuzers” designs that never went beyond paper, but for some equally gorgeous beasties from the Austro-Hungarian Empire, check out )

  2. Kristin

    I feel it is rather important in discussing the German ships to note—as Franz Hipper did—that the overly-sensitive British bursters did more to save the German Battle Cruisers and Battleships than did their armour, magazine discipline, or internal subdivision. Lyddite was a powerful explosive, but it was overly sensitive to shock—British APC generally exploded after penetrating about one-half their calibre thickness, well before the fuse would have detonated the shell.

    Given the number of hits HM ships scored, it seems likely that had even half of those hits seen the British shells perform as intended, Germans losses would have been greater. Seydlitz, for one, might not have survived turret hits.

    I should think it quite clear that the obsession with “Speed in All Things, and in All Ways” of the Royal Navy’s Battle Cruiser Force was a principal contributory factor in loss of the three Battle Cruisers. Of course, lost in all the finger-pointing about thin armour is the fact that the German 12-Inch APC could defeat ANY British turret roof or protective deck armour—including that on the most heavily-armoured Battleships. Still, it is true that the Grand Fleet’s Battleships under the temporary command of the BCF—the Queen Elizabeth-Class—took as severe a pounding from the High Seas Fleet (and its Scouting Force) as the Battlecruisers, without losing a ship.

    I think it not entirely accurate, therefore, to credit the German Battle Cruisers with superior “toughness”, as a blanket statement. Had Seydlitz taken a Greenboy to her wing turret, the results might well have been as awesome as the hit on Queen Mary. The Germans suffered exactly the same turret fire and near-magazine-loss as the British at Dogger Bank. The difference was that the Germans learnt the lessons presented, while the British did not.

    • padresteve

      Thank you for your reply. You have added some important and relevant information that for want of time I left out. You are very probably correct about what might have happened to Seydlitz had a different type of shell been used. But as you also said, the Germans had learned the lessons and tragically the Royal Navy hadn’t. Thank you again for your comments and expertise on the subject.

    • Winnie SC

      “Had Seydlitz taken a [not then extant] Greenboy to her wing turret, the results might well have been as awesome as the hit on Queen Mary.”

      Yes, and if your aunt had balls, she’d be your uncle.

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