The battleship USS North Carolina

The battleship USS North Carolina

The USS North Carolina’s underwater defence was one of the strongest points of this otherwise outstanding ship. The hull was divided into 22 main compartments (sections), these in turn divided by 21 watertight solid cross bulkheads (without culverts) extending from the triple bottom to the upper deck. As with older battleships, the North Carolina owed its ‘unsinkability’ to its five hull sections – in practice this meant that even the complete flooding of any two out of five hull’s sections would not result in the loss of the ship. Lengthwise the battleship had a triple bottom designed to protect it from exploding mines and deep-set torpedoes. It was also a foundation for boilers, machines, generators and other mechanical equipment located near the boiler room and engine room. The tanks of the triple bottom were filled with fuel or ballast water.
Underwater site protection system consisted of five light, flexible longitudinal bulkheads and an up-to-date anti-torpedo bulge. The space between particular bulkheads was used as fuel or ballast water tanks, increasing the defence value of the entire system. The two peripheral compartments were always left empty (although it was possible to flood it with water, e.g. to counter-ballast the ship) and the three inner compartments were filled with liquid (fuel or water). According to the design, the minimal toughness point for the board defence system were 317 kg torpedoes filled with pure TNT, in practice however, the system could stop much more powerful torpedoes.

North Carolina, 1945. Visualization 3D: Stefan Dramiński


The layered underwater protection system proved to be the best possible solution against underwater weapons for large ships. It was effective, easy to repair and it provided the ship with the possibility of balancing any list quickly by flooding the appropriate tanks on the opposite side, and if all the bulkheads were damaged, it effectively reduced the scope of combat damage, an incredibly important feature for emergency squads. The system passed the test on September 15, 1942 when the USS North Carolina was hit by a powerful 95-shiki torpedo (550kg head filled with Hexyl – heksanitro-diphenylamine – and pure TNT – trinitrotoluene)9  launched from a Japanese I-15 submarine. The explosion tore open a large hole near turret number 1, at a location where the hull narrowing made the bulkhead system narrow as well (in addition there were only four bulkheads in this area). However, despite an area some 60-square meters being damaged, only a couple of compartments aside from the main anti-torpedo bulkhead were flooded (longitudinal bulkhead number 4). Only a total of 970 ts of water flooded the ship’s hull, and its flow brought about a 5.5 degree list, soon balanced by flooding tanks on the opposite board. Despite being hit, the damaged USS North Carolina remained at operational readiness and in line (although turret number 1 could be used only in extreme necessity). In comparison, when in December 1943 the big Japanese battleship Yamato was hit by a Mark 14 torpedo (270 kg of TNT only) launched from an American submarine the USS Skate, some 3000 ts of water flooded the hull although the explosion took place at the widest and thus best protected section of the ship’s hull!

Propulsion

In the early 1930s, the US Navy resumed development of reliable and damage-resistant steam turbine propulsion. While designing new motive units, years’ of experience with high-pressure steam boilers proved very useful. The Americans were constantly up-rating the engine rooms of their ships improving energy efficiency, thus increasing endurance for a given fuel supply. As there was a need to achieve huge power, the only option was to make use of the traditional propulsion arrangements, yet which were different from what was used by other countries. The key to the American’s success was the development of holicoidal, two-stage reduction gear coupled with high-speed steam turbines built by the General Electric Co. This solution enabled the designers to keep propeller rotations within limits acceptable from the hydrodynamic point of view. High-speed turbines were easily powered by high-specs steam (pressure, temperature), which, in turn, made it possible to use high-pressure steam boilers. The outstanding specifications of the latest generation of US Navy battleship engine rooms was made possible by progress in the science of metallurgy. The up-to-date construction of all the propulsion system’s elements made it possible to greatly overload the engine room. An advantage of all US Navy’s battleships built from 1920s on, was the implementation of 450 V tri-phase alternating current to power the machines.
The USS North Carolina’s engine room was of a “clean” type (Melville-MacAlpine system). That means that most of the machines, like turbines or motor-generator, were put into special containers. This increased the staff’s work comfort and safety and, to some extent, reduced bothersome vibrations. The entire power unit was placed in five compartments, divided by solid transverse bulkheads (without culverts). Four compartments housed two Babcock & Wilcox boilers each, adjacent General Electric steam turbine (with 1150 kW tri-phase alternating power generator and a switchboard) and a condenser. Each of the water tube, three shaft boilers produced steam at a pressure of 40.43 kG/cm2 and a temperature of 454.4 degrees centigrade. There was an auxiliary power room in the fifth compartment, together with spare 200kW combustion turbo-generators. The turbines were coupled with four asymmetrically placed propeller shafts (both propeller’s type and radius altered during the ship’s service). Propulsion control and supervision was run from the Power Room Control Centre located in engine room number 3. This automated room was at the same time the main Damage Control Centre.

Shielded Bofors mount with some elements shown as half-transparent for better view. Note the ammunition clips kept on the inner sides of the shield. Visualization 3D: Stefan Dramiński


When developing full engine room power of 121,000 SHP, the battleship could reach the speed of 27 knots in deep waters. The up-to-date construction, however, made possible one-hour overload by 20-25% to reach the power of 145,000 SHP and the maximum speed of 29 knots at the displacement of 44,794.7 ts. Unfortunately problems with vibrations caused by, amongst other things, insufficient care while constructing shafts line and choosing propellers, speeds exceeding 27 knots were shunned (the fastest recorded battleship speed at combat displacement reached 27.3 knots). The new battleships’ range was outstanding: at the maximum fuel reserve of 6859.7 ts USS North Carolina could travel 17,450 nautical miles at 15 knots without re-fueling.

Armament


406 mm (16”) L/45 Mk-6 guns – were the main weapons of the battleships of the North Carolina class (and also the following South Dakota class). Designed in 1936, the Mk-6 guns were easily among the best heavy naval guns produced – in deck penetration they were unmatched – not for nothing were they nicknamed „deck smashers”. Although they are not the biggest caliber guns ever – in the 20th century they were second only to 460 mm (18.1”) Japanese guns from the Yamato class battleships – they had the best ballistic specifications and records in their class while being very quick firing for such a big caliber. Launching Mk-8 armor-piercing hard-capped projectiles (APC) they were able to penetrate 10-meter thick reinforced concrete or pierce 664mm vertical armored plate made of A3 class face-hardened armor from a distance of 9.1 km. There were Mk-21 fuzes used with a delay of 0.033 second. 38 mm thick armored plate at the hit angle of 0 degrees or 9.5 mm at 65 degrees was sufficient to detonate each of the fuzes. […]

 

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North Carolina

 

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