They were never ordered due to signing of the Washington Naval Treaty in 1922, which limited the size and armament of battleships to 35,000 long tons (36,000 t) and guns no bigger than 16 inches (406 mm).

In 1916 the US had declared its intention to create a Navy "second to none"; Congress had authorized the building of a large number of battleships and battlecruisers.

Seven more were intended to be laid down in 1920–21, six of these were the very large and powerful South Dakota class, armed with twelve 16-inch guns.

The battleship designs were given letters of the alphabet from L through N, with the use of triple or double gun turrets shown by 3 or 2 respectively.

[5] 'M2' and 'M3' sacrificed fire directly astern by moving the rear turret(s) amidships in order to save weight by shortening the length of the armoured citadel.

This provided a better and more stable foundation for fire-control equipment, greatly improved accommodation and protection from the weather.

The turbines would have been powered by small-tube boilers intended to produce a total of 56,000 shaft horsepower (42,000 kW).

[11] The choice of a high muzzle velocity with a relatively lighter shell was taken from the German practice; it ran counter to previous British guns such as the BL 15-inch Mark I gun of 42-calibre length which were lower-muzzle-velocity weapons firing heavy shells.

Naval historian John Campbell quotes the projectile weight as 2,916 pounds (1,323 kg) fired at a muzzle velocity of 2,650 ft/s (810 m/s),[14] but Alan Raven and John Roberts cite a 2,837-pound (1,287 kg) shell fired at a muzzle velocity of 2,700 ft/s (820 m/s).

[16][17] The N3s carried a secondary armament of sixteen BL 6-inch Mk XXII guns in superfiring twin turrets.

They fired a 50-pound (23 kg) high explosive shell at a muzzle velocity of 2,457 ft/s (749 m/s) at a rate of eight to twelve rounds per minute.

[21] The ships were intended to carry four 10-barreled mountings[Note 1] for the 40-millimetre (1.6 in) QF 2-pounder gun (commonly known as a pom-pom), two abaft the funnels and two at the stern.

[22] Like previous classes of British battleships, a pair of submerged, broadside-firing torpedo tubes were planned for these ships.

Use of this system was pioneered by contemporary U.S. Navy battleship designs starting with the Nevada class.

This system of protection required that the armoured citadel have enough reserve buoyancy to keep the ship stable even if the rest of the hull was riddled by gunfire.

It extended forward over the torpedo compartment which had a separate transverse bulkhead protecting it that was 9 inches (229 mm) thick.

The fire-control director atop the conning tower was protected by an armoured hood 4 to 6 inches thick.

[17] The anti-torpedo bulges of the N3 were internal to the hull and were intended to withstand the explosion of a 750-pound (340 kg) torpedo warhead.

[26] Postwar tests done on a replica of this system showed that filling the buoyancy space with water rather than the sealed steel crushing tubes as used in Hood was just as effective and weighed less.