N3 class battleship
Encyclopedia
The N3 class was a dreadnought battleship class designed for the Royal Navy
after World War I
, incorporating all the lessons learned from that conflict. They were very similar in design to the s, but had larger guns and thicker armour. They were never ordered due to signing of the Washington Naval Treaty
in 1922, which limited the size and armament of battleships to 35000 long tons (35,561.8 t) tons and no gun bigger than 16 inches (41 cm).
). Two improved Revenge-class hulls were rebuilt into the two s by the Royal Navy during the war. The only new capital ships laid down
during the war were the s. Their design had been called into question after the Battle of Jutland
in 1916 and three ships of this class were cancelled, leaving only to be completed to a modified design.
The US plan had been delayed by the wartime need to build smaller vessels. Nevertheless, estimates by the Admiralty were that by the early 1920s the Royal Navy would be behind in ships. By the beginning of 1920, the Americans had completed one battleship since the end of World War I and and had five more building. Seven more were intended to be laid down in 1920–21, six of these were the very large and powerful , armed with twelve 16-inch guns. The Japanese had finished one battleship since the end of the war and had three more under construction. To correct this state of affairs, the Admiralty initially planned to build three battleships and one battlecruiser in Fiscal Year (FY) 1921–22 and again in FY 1922–23, but this was changed to four s to be built first, presumably to be followed by the same number of battleships the following year.
A pair of designs were prepared in June 1920, derived from the U-4 design of 1914, of ships with displacements of about 50000 long tons (50,802.5 t) and armed with eight or nine guns, in four twin or three triple gun turret
s mounting a new 18 inches (46 cm) gun then under development. The only limitation of the design was the inability to use British dockyards and pass through the Suez Canal
. The most unusual feature of these designs was that none of the turrets were superfiring
, presumably to keep the centre of gravity as low as possible and avoid the extra weight required for tall, superfiring barbette
s.
The designs were revised in October and split into separate battleship and battlecruiser designs. 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. Both 'L2' and 'L3' had superfiring guns and the armour was reduced to a 15 inches (38 cm) inclined waterline
belt
while the main armoured deck was 8 inches (20 cm) thick (9 inches (23 cm) where it sloped to meet the belt). They both had a designed speed of 25 knots (13.6 m/s) and had transom sterns. 'L2' displaced 52100 long tons (52,936.2 t), but 'L3' was a thousand tons lighter. 'M2' and 'M3' followed in November and December and were very different from the earlier designs.
'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. Compared to the earlier, more conventional, designs, 'M2' saved 1540 LT and 'M3' 1740 LT. More weight was saved by reducing the designed speed to 23–23.5 kn (12.5–12.8 ) and using only two propeller shafts, although it was thought that this would improve manoeuvering power over four smaller propellers. These changes saved 4350 LT for 'M2' and 5000 LT for 'M3' over their predecessors. A lengthened version of 'M3' was chosen for further development as N3 and approved in November 1921.
The N3 battleships were significantly larger than their predecessors of the . They had an overall length of 820 feet (249.9 m), a beam
of 106 feet (32.3 m), and a draught of 33 feet (10.1 m) at deep load. They would have displaced about 48500 long tons (49,278.4 t), nearly double the displacement of the older ships. They had a complete double bottom
7 feet (2.1 m) deep.
The ships would have had two geared steam turbine
sets, each of which drove one propeller shaft, in two engine rooms forward of the boiler rooms. This allowed the funnel
to be placed further aft and increased the ability of the rear turret to fire to the rear. The turbines would have been powered by small-tube boilers
intended to produce a total of 56000 shp. The ships' maximum speed would have been about 23 knots.
Housing the main armament in triple turrets was new to the Royal Navy though British companies had been involved in the production of triple gun turret designs for other navies. 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.
of 2650 ft/s (807.7 m/s), but Alan Raven and John Roberts cite a 2837 pounds (1,286.8 kg) fired at a muzzle velocity
of 2700 ft/s (823 m/s). The N3s carried a secondary armament of sixteen BL 6-inch Mk XXII guns
in superfiring
twin turrets. Four turrets were sited around the forward superstructure and four at the stern. The guns could elevate between –5° and +60°. They fired 100 pounds (45.4 kg) projectiles at a muzzle velocity of 2945 ft/s (897.6 m/s). Their maximum range was 25800 yd (23,591.5 m) at 45° elevation. Their rate of fire was five rounds per minute.
An anti-aircraft
battery of six QF 4.7-inch Mk VIII guns
was included. They had a maximum depression of -5° and a maximum elevation of 90°. They fired a 50 pounds (22.7 kg) high explosive shell at a muzzle velocity of 2457 ft/s (748.9 m/s) at a rate of eight to twelve rounds per minute. The guns had a maximum ceiling of 32000 ft (9,753.6 m), but an effective range of much less. The ships were intended to carry four 10-barreled mountings for the 40 millimetres (1.6 in) QF 2-pounder Mk VIII gun
(commonly known as a pom-pom), two abaft the funnels and two at the stern. Each barrel was provided with 1300 rounds of ammunition. The gun fired a 40 millimetres (1.6 in) 0.91 pound (0.4127690567 kg) shell at a muzzle velocity of 1920 ft/s (585.2 m/s) to a distance of 3800 yards (3,474.7 m). The gun's rate of fire was approximately 96–98 rounds per minute.
Like previous classes of British battlecruisers, a pair of submerged, broadside-firing torpedo tube
s were planned for these ships. Their compartment was located just forward of the 'A' shell room on the platform deck. Six 24.5 inches (62.2 cm) torpedoes per tube were to be carried in peace-time, but this would increase to eight in wartime. These Mark I torpedoes had a warhead of 743 pounds (337 kg) of TNT and were powered by oxygen-enriched air. They had two speed settings which governed their range: either 15000 yards (13,716 m) at 35 knots (19.1 m/s), or 20000 yards (18,288 m) at 30 knots (16.3 m/s).
in an armoured hood. Each main gun turret was provided with a 41 feet (12.5 m) coincidence rangefinder
in an armoured housing on the turret roof. The secondary armament was primarily controlled by two DCTs mounted on each side of the bridge. The anti-aircraft guns were controlled by a high-angle control system mounted on the mizzenmast. Each pom-pom mount had its own director and there was also a height-finder aft. Two 15 feet (4.6 m) torpedo rangefinders were located on the sides of the funnels.
was the use of the all or nothing protection scheme in the N3s and G3s. Medium-thickness armour had proven to be useless in stopping heavy-calibre shells during World War I so the vital areas of the ship were protected by the thickest possible armour and the rest of the ship was left unarmoured. Use of this system was pioneered by contemporary U.S. Navy battleship designs starting with the . However, this system of protection required that the armoured citadel should have enough reserve buoyancy to keep the ship stable even if the rest of the hull was riddled by gunfire.
The waterline belt of the N3 had a maximum thickness of 15 inches (38 cm) thick with the top of the armour angled outwards. This angle increased the armor's relative thickness to horizontal, close-range fire, albeit at the cost of reducing its relative height which increased the chance of plunging shellfire going over or under it. It ran some 463 feet (141.1 m), from 9 feet (2.7 m) forward of 'A' barbette to the rear of the after 6-inch magazine
. For about 115 feet (35.1 m), it reduced to 13.5 inches (34 cm) over the engine and boiler rooms. The belt had a height of 14 in 3 in (4.34 m), of which 4 in 6 in (1.37 m) was below the designed waterline. The lower edge of the belt abreast the magazines was continued down another 3 foot (0.9144 m) by a 4 inches (10 cm) thickness of high-tensile steel inclined at 36° to prevent a shell from reaching the magazines via a wave trough at high speed. The ends of the belt terminated in 14 inches (36 cm) tranverse bulkhead
s. The 8 inches (20 cm) armoured deck matched the length of the waterline belt and sloped down to meet the upper edge of the belt. It extended forward over the torpedo compartment which had a separate transverse bulkhead protecting it that was 9 inches (23 cm) thick. The steering gear was protected by a deck and bulkhead 6 inches (15 cm) thick.
The turret faces were 18 inches (46 cm) thick while their sides were probably 14 inches (36 cm) in thickness, and the roof was 8 inches thick. The armour of the barbettes and the conning tower
was 15 inches thick and the conning tower's communications tube to the upper deck was 8 inches thick. The fire-control director atop the conning tower was protected by an armoured hood 4 to 6 inches thick.
The anti-torpedo bulge
s of the N3 were internal to the hull and were intended to withstand the explosion of a 750 pounds (340.2 kg) torpedo warhead
. They consisted of an outer air space, an inner buoyancy space and the 2 inches (5 cm) thick torpedo bulkhead
. The bulkhead was situated about 16 feet (4.9 m) inboard from the side of the ship. 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 was just as effective and weighed less.
, an arms limitation
treaty under negotiation at the time, forbade construction of any ship larger than 35,000 tons. Many of the aspects of their design ultimately were incorporated into the two s, and they are often described as being a cut-down N3. Indeed, the Nelsons received the design designation 'O3', marking them as next in the design sequence, although they used the guns intended for the G3 battlecruisers for cost reasons and to comply with the Treaty's 16-inch limitation on main armament.
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...
after World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
, incorporating all the lessons learned from that conflict. They were very similar in design to the s, but had larger guns and thicker armour. They were never ordered due to signing of the Washington Naval Treaty
Washington Naval Treaty
The Washington Naval Treaty, also known as the Five-Power Treaty, was an attempt to cap and limit, and "prevent 'further' costly escalation" of the naval arms race that had begun after World War I between various International powers, each of which had significant naval fleets. The treaty was...
in 1922, which limited the size and armament of battleships to 35000 long tons (35,561.8 t) tons and no gun bigger than 16 inches (41 cm).
Background
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. In response, the Japanese government also began a large programme of warship building (the 8-8 fleetEight-eight fleet
The was a Japanese naval strategy formulated for the development of the Imperial Japanese Navy in the first quarter of the 20th century, which laid down that the Japanese navy should include eight first-class battleships and eight armoured cruisers or battlecruisers.-History and development:The...
). Two improved Revenge-class hulls were rebuilt into the two s by the Royal Navy during the war. The only new capital ships laid down
Keel
In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...
during the war were the s. Their design had been called into question after the Battle of Jutland
Battle of Jutland
The Battle of Jutland was a naval battle between the British Royal Navy's Grand Fleet and the Imperial German Navy's High Seas Fleet during the First World War. The battle was fought on 31 May and 1 June 1916 in the North Sea near Jutland, Denmark. It was the largest naval battle and the only...
in 1916 and three ships of this class were cancelled, leaving only to be completed to a modified design.
The US plan had been delayed by the wartime need to build smaller vessels. Nevertheless, estimates by the Admiralty were that by the early 1920s the Royal Navy would be behind in ships. By the beginning of 1920, the Americans had completed one battleship since the end of World War I and and had five more building. Seven more were intended to be laid down in 1920–21, six of these were the very large and powerful , armed with twelve 16-inch guns. The Japanese had finished one battleship since the end of the war and had three more under construction. To correct this state of affairs, the Admiralty initially planned to build three battleships and one battlecruiser in Fiscal Year (FY) 1921–22 and again in FY 1922–23, but this was changed to four s to be built first, presumably to be followed by the same number of battleships the following year.
A pair of designs were prepared in June 1920, derived from the U-4 design of 1914, of ships with displacements of about 50000 long tons (50,802.5 t) and armed with eight or nine guns, in four twin or three triple gun turret
Gun turret
A gun turret is a weapon mount that protects the crew or mechanism of a projectile-firing weapon and at the same time lets the weapon be aimed and fired in many directions.The turret is also a rotating weapon platform...
s mounting a new 18 inches (46 cm) gun then under development. The only limitation of the design was the inability to use British dockyards and pass through the Suez Canal
Suez Canal
The Suez Canal , also known by the nickname "The Highway to India", is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea and the Red Sea. Opened in November 1869 after 10 years of construction work, it allows water transportation between Europe and Asia without navigation...
. The most unusual feature of these designs was that none of the turrets were superfiring
Superfire
The idea of superfire is to locate two turrets in a row, one behind the other, but with the second turret located above the one in front so that the second turret could fire over the first...
, presumably to keep the centre of gravity as low as possible and avoid the extra weight required for tall, superfiring barbette
Barbette
A barbette is a protective circular armour feature around a cannon or heavy artillery gun. The name comes from the French phrase en barbette referring to the practice of firing a field gun over a parapet rather than through an opening . The former gives better angles of fire but less protection...
s.
The designs were revised in October and split into separate battleship and battlecruiser designs. 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. Both 'L2' and 'L3' had superfiring guns and the armour was reduced to a 15 inches (38 cm) inclined waterline
Waterline
The term "waterline" generally refers to the line where the hull of a ship meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft of the ship and the legal limit to which a ship...
belt
Belt armor
Belt armor is a layer of heavy metal armor plated on to or within outer hulls of warships, typically on battleships, battlecruisers and cruisers, and on aircraft carriers converted from those types of ships....
while the main armoured deck was 8 inches (20 cm) thick (9 inches (23 cm) where it sloped to meet the belt). They both had a designed speed of 25 knots (13.6 m/s) and had transom sterns. 'L2' displaced 52100 long tons (52,936.2 t), but 'L3' was a thousand tons lighter. 'M2' and 'M3' followed in November and December and were very different from the earlier designs.
'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. Compared to the earlier, more conventional, designs, 'M2' saved 1540 LT and 'M3' 1740 LT. More weight was saved by reducing the designed speed to 23–23.5 kn (12.5–12.8 ) and using only two propeller shafts, although it was thought that this would improve manoeuvering power over four smaller propellers. These changes saved 4350 LT for 'M2' and 5000 LT for 'M3' over their predecessors. A lengthened version of 'M3' was chosen for further development as N3 and approved in November 1921.
Description
Most noticeable of the N3 design was the concentration of the main battery forward of the bridge and machinery spaces. A related feature of the design was the tower bridge structure behind the first two gun turrets. This provided a better and more stable foundation for fire-control equipment, greatly improved accommodation and protection from the weather.The N3 battleships were significantly larger than their predecessors of the . They had an overall length of 820 feet (249.9 m), a beam
Beam (nautical)
The beam of a ship is its width at the widest point. Generally speaking, the wider the beam of a ship , the more initial stability it has, at expense of reserve stability in the event of a capsize, where more energy is required to right the vessel from its inverted position...
of 106 feet (32.3 m), and a draught of 33 feet (10.1 m) at deep load. They would have displaced about 48500 long tons (49,278.4 t), nearly double the displacement of the older ships. They had a complete double bottom
Double bottom
A double bottom is a ship hull design and construction method where the bottom of the ship has two complete layers of watertight hull surface: one outer layer forming the normal hull of the ship, and a second inner hull which is somewhat higher in the ship, perhaps a few feet, which forms a...
7 feet (2.1 m) deep.
The ships would have had two geared steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
sets, each of which drove one propeller shaft, in two engine rooms forward of the boiler rooms. This allowed the funnel
Funnel (ship)
A funnel is the smokestack or chimney on a ship used to expel boiler steam and smoke or engine exhaust. They can also be known in as stacks.-Purpose:...
to be placed further aft and increased the ability of the rear turret to fire to the rear. The turbines would have been powered by small-tube boilers
Water-tube boiler
A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes...
intended to produce a total of 56000 shp. The ships' maximum speed would have been about 23 knots.
Housing the main armament in triple turrets was new to the Royal Navy though British companies had been involved in the production of triple gun turret designs for other navies. 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
Caliber (artillery)
In artillery, caliber or calibredifference in British English and American English spelling is the internal diameter of a gun barrel, or by extension a relative measure of the length....
length which were lower-muzzle-velocity weapons firing heavy shells.
Armament
The N3 design mounted nine 45-calibre BL 18-inch guns in three triple gun turrets, designated 'A', 'B', and 'X' from front to rear. The guns had a maximum elevation of 40°. As none of these guns was ever completed and test-fired, sources differ on their exact specifications. Naval historian John Campbell quotes the projectile weight as 2916 pounds (1,322.7 kg) fired at a muzzle velocityMuzzle velocity
Muzzle velocity is the speed a projectile has at the moment it leaves the muzzle of the gun. Muzzle velocities range from approximately to in black powder muskets , to more than in modern rifles with high-performance cartridges such as the .220 Swift and .204 Ruger, all the way to for tank guns...
of 2650 ft/s (807.7 m/s), but Alan Raven and John Roberts cite a 2837 pounds (1,286.8 kg) fired at a muzzle velocity
Muzzle velocity
Muzzle velocity is the speed a projectile has at the moment it leaves the muzzle of the gun. Muzzle velocities range from approximately to in black powder muskets , to more than in modern rifles with high-performance cartridges such as the .220 Swift and .204 Ruger, all the way to for tank guns...
of 2700 ft/s (823 m/s). The N3s carried a secondary armament of sixteen BL 6-inch Mk XXII guns
BL 6 inch Mk XXII naval gun
The BL 6-inch Mk XXII gun was a British high-velocity 6-inch 50-calibre wire-wound naval gun used as secondary armament on the two Nelson class battleships, serving throughout World War II.-Ammunition:...
in superfiring
Superfire
The idea of superfire is to locate two turrets in a row, one behind the other, but with the second turret located above the one in front so that the second turret could fire over the first...
twin turrets. Four turrets were sited around the forward superstructure and four at the stern. The guns could elevate between –5° and +60°. They fired 100 pounds (45.4 kg) projectiles at a muzzle velocity of 2945 ft/s (897.6 m/s). Their maximum range was 25800 yd (23,591.5 m) at 45° elevation. Their rate of fire was five rounds per minute.
An anti-aircraft
Anti-aircraft warfare
NATO defines air defence as "all measures designed to nullify or reduce the effectiveness of hostile air action." They include ground and air based weapon systems, associated sensor systems, command and control arrangements and passive measures. It may be to protect naval, ground and air forces...
battery of six QF 4.7-inch Mk VIII guns
QF 4.7 inch Mk VIII naval gun
The QF 4.7 inch Gun Mark VIII was a British naval anti-aircraft gun designed in the 1920s for the Royal Navy. It was mounted on the two , two of the three s and the Australian submarine tender HMAS Albatross .-External links:...
was included. They had a maximum depression of -5° and a maximum elevation of 90°. They fired a 50 pounds (22.7 kg) high explosive shell at a muzzle velocity of 2457 ft/s (748.9 m/s) at a rate of eight to twelve rounds per minute. The guns had a maximum ceiling of 32000 ft (9,753.6 m), but an effective range of much less. The ships were intended to carry four 10-barreled mountings for the 40 millimetres (1.6 in) QF 2-pounder Mk VIII gun
QF 2 pounder naval gun
The 2-pounder gun, officially designated the QF 2-pounder and universally known as the pom-pom, was a 1.575 inch British autocannon, used famously as an anti-aircraft gun by the Royal Navy. The name came from the sound that the original models make when firing...
(commonly known as a pom-pom), two abaft the funnels and two at the stern. Each barrel was provided with 1300 rounds of ammunition. The gun fired a 40 millimetres (1.6 in) 0.91 pound (0.4127690567 kg) shell at a muzzle velocity of 1920 ft/s (585.2 m/s) to a distance of 3800 yards (3,474.7 m). The gun's rate of fire was approximately 96–98 rounds per minute.
Like previous classes of British battlecruisers, a pair of submerged, broadside-firing torpedo tube
Torpedo tube
A torpedo tube is a device for launching torpedoes. There are two main types of torpedo tube: underwater tubes fitted to submarines and some surface ships, and deck-mounted units installed aboard surface vessels...
s were planned for these ships. Their compartment was located just forward of the 'A' shell room on the platform deck. Six 24.5 inches (62.2 cm) torpedoes per tube were to be carried in peace-time, but this would increase to eight in wartime. These Mark I torpedoes had a warhead of 743 pounds (337 kg) of TNT and were powered by oxygen-enriched air. They had two speed settings which governed their range: either 15000 yards (13,716 m) at 35 knots (19.1 m/s), or 20000 yards (18,288 m) at 30 knots (16.3 m/s).
Fire-control
The main guns of the battleships could be controlled from any of the two director-control towers (DCT). The primary DCT was mounted at the top of the forward superstructure. Another was mounted on the roof of the conning towerConning tower
A conning tower is a raised platform on a ship or submarine, often armored, from which an officer can con the vessel; i.e., give directions to the helmsman. It is usually located as high on the ship as practical, to give the conning team good visibility....
in an armoured hood. Each main gun turret was provided with a 41 feet (12.5 m) coincidence rangefinder
Coincidence rangefinder
A coincidence rangefinder is a type of rangefinder that uses mechanical and optical principles to allow an operator to determine the distance to a visible object....
in an armoured housing on the turret roof. The secondary armament was primarily controlled by two DCTs mounted on each side of the bridge. The anti-aircraft guns were controlled by a high-angle control system mounted on the mizzenmast. Each pom-pom mount had its own director and there was also a height-finder aft. Two 15 feet (4.6 m) torpedo rangefinders were located on the sides of the funnels.
Armour
A first for any British dreadnoughtDreadnought
The dreadnought was the predominant type of 20th-century battleship. The first of the kind, the Royal Navy's had such an impact when launched in 1906 that similar battleships built after her were referred to as "dreadnoughts", and earlier battleships became known as pre-dreadnoughts...
was the use of the all or nothing protection scheme in the N3s and G3s. Medium-thickness armour had proven to be useless in stopping heavy-calibre shells during World War I so the vital areas of the ship were protected by the thickest possible armour and the rest of the ship was left unarmoured. Use of this system was pioneered by contemporary U.S. Navy battleship designs starting with the . However, this system of protection required that the armoured citadel should have enough reserve buoyancy to keep the ship stable even if the rest of the hull was riddled by gunfire.
The waterline belt of the N3 had a maximum thickness of 15 inches (38 cm) thick with the top of the armour angled outwards. This angle increased the armor's relative thickness to horizontal, close-range fire, albeit at the cost of reducing its relative height which increased the chance of plunging shellfire going over or under it. It ran some 463 feet (141.1 m), from 9 feet (2.7 m) forward of 'A' barbette to the rear of the after 6-inch magazine
Magazine (artillery)
Magazine is the name for an item or place within which ammunition is stored. It is taken from the Arabic word "makahazin" meaning "warehouse".-Ammunition storage areas:...
. For about 115 feet (35.1 m), it reduced to 13.5 inches (34 cm) over the engine and boiler rooms. The belt had a height of 14 in 3 in (4.34 m), of which 4 in 6 in (1.37 m) was below the designed waterline. The lower edge of the belt abreast the magazines was continued down another 3 foot (0.9144 m) by a 4 inches (10 cm) thickness of high-tensile steel inclined at 36° to prevent a shell from reaching the magazines via a wave trough at high speed. The ends of the belt terminated in 14 inches (36 cm) tranverse bulkhead
Bulkhead (partition)
A bulkhead is an upright wall within the hull of a ship or within the fuselage of an airplane. Other kinds of partition elements within a ship are decks and deckheads.-Etymology:...
s. The 8 inches (20 cm) armoured deck matched the length of the waterline belt and sloped down to meet the upper edge of the belt. It extended forward over the torpedo compartment which had a separate transverse bulkhead protecting it that was 9 inches (23 cm) thick. The steering gear was protected by a deck and bulkhead 6 inches (15 cm) thick.
The turret faces were 18 inches (46 cm) thick while their sides were probably 14 inches (36 cm) in thickness, and the roof was 8 inches thick. The armour of the barbettes and the conning tower
Conning tower
A conning tower is a raised platform on a ship or submarine, often armored, from which an officer can con the vessel; i.e., give directions to the helmsman. It is usually located as high on the ship as practical, to give the conning team good visibility....
was 15 inches thick and the conning tower's communications tube to the upper deck was 8 inches thick. The fire-control director atop the conning tower was protected by an armoured hood 4 to 6 inches thick.
The anti-torpedo bulge
Anti-torpedo bulge
The anti-torpedo bulge is a form of passive defence against naval torpedoes that featured in warship construction in the period between the First and Second World Wars.-Theory and form:...
s of the N3 were internal to the hull and were intended to withstand the explosion of a 750 pounds (340.2 kg) torpedo warhead
Warhead
The term warhead refers to the explosive material and detonator that is delivered by a missile, rocket, or torpedo.- Etymology :During the early development of naval torpedoes, they could be equipped with an inert payload that was intended for use during training, test firing and exercises. This...
. They consisted of an outer air space, an inner buoyancy space and the 2 inches (5 cm) thick torpedo bulkhead
Torpedo bulkhead
A torpedo bulkhead is a type of armor common on the more heavily armored warships, especially battleships and battlecruisers of the early 20th century. It is designed to keep the ship afloat even if the hull was struck underneath the belt armor by a shell or by a torpedo...
. The bulkhead was situated about 16 feet (4.9 m) inboard from the side of the ship. 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 was just as effective and weighed less.
Cancellation
The four N3 battleships were never ordered because the Washington Naval TreatyWashington Naval Treaty
The Washington Naval Treaty, also known as the Five-Power Treaty, was an attempt to cap and limit, and "prevent 'further' costly escalation" of the naval arms race that had begun after World War I between various International powers, each of which had significant naval fleets. The treaty was...
, an arms limitation
Arms control
Arms control is an umbrella term for restrictions upon the development, production, stockpiling, proliferation, and usage of weapons, especially weapons of mass destruction...
treaty under negotiation at the time, forbade construction of any ship larger than 35,000 tons. Many of the aspects of their design ultimately were incorporated into the two s, and they are often described as being a cut-down N3. Indeed, the Nelsons received the design designation 'O3', marking them as next in the design sequence, although they used the guns intended for the G3 battlecruisers for cost reasons and to comply with the Treaty's 16-inch limitation on main armament.