As many do, sixfrigates recently inquired about her design, so here's the explanation, bells, whistles and all. To skip the commentary on post-WWI, pre-Washington Treaty foreign relations and battleships, go to the last paragraph.
Nelson and Rodney were the children of a long line of designs which aimed to outdo all at a time of heightened post-World War I tensions between Britain, Japan and the United States. In essence, after the catastrophe of WWI which knocked Germany out of the empire game, Japan and the U.S. took up the gauntlet, wanting trade and trade security in the Pacific and Asia. With Britain, as usual, rocking trade monopolies in the region, there was quite a large elephant in the room. Initially, Japan had two Nagato-class battleships, two Tosa-class battleships, and a total of four Amagi-class battlecruisers in the works. All were very modern and very capable ships, carrying bloody scary 16-inch guns.
Now in 1916, Woodrow Wilson, who history seems to remember as that bloke who pushed for peace with his League of Nations, got a plan through for a fleet of 16 capitol ships. Then, in 1919, he got another plan through to build another set of 16 far more powerful vessels. In conversation with his close friend and adviser, Col. Edward House, Wilson said something along the lines of: "Let us build a Navy bigger than hers [Britain] and do what we please.” Go figure, history shall be kind. At any rate, America soon had four Colorado-class battleships underway and the first of six South Dakota-class battleships, mounting twelve 16" guns [click]. They also had six Lexington-class battlecruisers planned, inspired by Hood, armed with eight 16" guns, while capable of 33 knots.
In response, Japan lined up an additional four fast battleships of a new Kii-class, mounting ten 16" guns while capable of nearly 30 knots, which would augment the four planned Amagi-class battlecruisers in an eight-eight fleet. A further four battleships known only as the Number 13-class would then have been built, with eight 18-inch guns and a top speed of 30 knots. Of these ships, many historians have expressed concurring thoughts to Naval architects William Garzke and Robert Dulin, who said, "These ships would have completely outclassed any European battleship". Now this was absolutely true and if you're beginning to think things were getting a little crazy, they were.
Enter Britain, with a bloody nose, an ice-pack for the headache and an encyclopedia of wartime experience. Four years of fighting the First World War had left its mark, but for a navy which had maintained dominion over the seas entire arguably since it's repulsion of the Spanish Armada in 1588, there were no plans for that to change. A design process began which aimed to see four N3-class battleships and four G3-class battlecruisers constructed, on top of the four Admiral-class battlecruisers already under construction (HMS Hood & Co.). The G3-class were to be capable of the 32 knot speed of the U.S. Lexington design, while themselves armed with nine 16" guns. However, in armour, these new ships of the Royal Navy would dwarf the Lexington-class and Japanese Amagi-class, boasting an 18° angled main belt reaching 14 inches, decks 8 inches and turret-faces of 17 inches, all on a deep load displacement of 54,000 long tons. To dispense with the South Dakota-class and more importantly the Japanese Number 13-class, the N3-class battleships were true brawlers. Though only capable of 23 knots, these titans of the line were to mount nine 18" guns in three triple turrets, all protected by an angled main belt 15 inches thick, decks 8 inches, turret faces 18 inches and bulkheads up to 14 inches.
These two classes already sound formidable, but the Royal Navy's designers had also hatched a brilliant scheme. Grouping the armament closer together and utilising the all or nothing principle would allow for the construction of a very heavily armoured citadel, recessed within the ships outer hull. Designers realised this structure could be made with enough buoyancy to alone float the ship. By simply moving the aft turret amidships, creating a shortened citadel, still buoyant enough to keep the entire vessel afloat, they reduced overall tonnage, vastly improved survivability, and crucially, stability when severely damaged.
Now the whole farce above, which was a full blown arms race, was supposedly ironed out by the Washington Naval Treaty in 1922. In reality, like Versailles for Europe, it was an agreed armistice for a set period of time. In my opinion, it very simply postponed the inevitable, a war involving Japan, America and the British Empire for influence in Asia. But back to battleships and at last sixfrigates question.
Japan had already built two 16" gun battleships in the Nagato-class. America's Colorado-class gave America the same. Britain, the world's greatest naval power, had no vessels boasting anything larger than 15" guns, though still formidable. This being recognised (and perhaps as compensation for agreeing to parity with the U.S. Fleet), Britain was permitted to construct two 16" gun vessels weighing no more than 35,000 tons.
Taking the finished design of the G3-class battlecruisers, it was down-scaled and reshuffled to create the Nelson-class battleship. To reduce the length of the former from 856 ft (260 m) to just 660 ft (201 m) for Nelson and Rodney, all main guns were placed forward of the bridge and conning tower. Doing this also allowed the all or nothing armour scheme with a shorter recessed citadel to be utilised. It saved weight which was crucial, but it also gave the increased survivability of the G3 design. For the Nelson-class, the maths was done for the worst case scenario, with the ends of the ship, bow and stern, blown off completely and open to the sea. Her spaced compartments were considered to be flooded and yet it was calculated that the ships would have retained a freeboard of around 8 feet. It sounds low but a number of German capitol ships after Jutland, SMS Seydlitz and friends, limped home with their bows effectively submerged, despite the stormy nature of the North Sea. Nelson and Rodney come in for a lot of grief with their bizarre configuration, but the simple truth is - it made sense. Retarded by treaty obligations, they were not the Gods that were the G3s, but they were heavily armed and capable of surviving grueling punishment. By WW2 they were old technology, but Rodney's guns still smashed through the thickest (flat 14.17") armour plates used on Bismarck. Going on that, it is certainly likely the guns of the G3-class, never mind the 18 inchers of the N3-class, would have penetrated the armour of their 1920s contemporaries.
