When is "new and improved" worse?
The strange case of the North Carolina and South Dakota class battleships
It’s been said that the South Dakota class were the best class of “treaty” battleship - that is, the best battleships built under the restrictive terms of the arms limitations treaties that held sway between World War I and World War II. I disagree. The North Carolina class that preceded them was better - and it’s a good example of how what’s advertised as “new and improved” sometimes really is just “new and changed.”
To begin with, it’s important to acknowledge how similar the two classes of battleship were, so similar that the differences between them are often overlooked. Both had the same main battery of nine 16”/45 guns in three triple turrets. Both ships of the North Carolina class and three of the ships of the South Dakota class had the same secondary battery of twenty 5”/38 dual-purpose guns in ten double turrets. Both were designed to be exactly the 35,000 “standard” tons mandated by treaty - and actually 45,000 tons fully loaded.
However, the South Dakota class was built to be more compact - fifty feet shorter overall, with the turrets closer together and the superstructure crowded more closely together. The North Carolina was a “leggier” vessel. The South Dakota had slightly more powerful engines and a slightly slower top speed.
So why make the ship shorter? The reason for this was that the Navy wanted the South Dakota class to be a “balanced” design. The North Carolina had 16” guns and was designed to resist 14” gunfire. A “balanced” design would be able to resist 16” gunfire. Making the ship shorter reduced the area that needed to be armored, which meant that the armor could be made thicker within the same fixed 35,000 ton mass budget. Overall, the armor of the South Dakota class was about 10% thicker over the most critical areas of the ship.
Torpedo trouble
The interior of the South Dakota class was cramped, as more machinery needed to be packed into a smaller space. However, the South Dakota couldn’t be made any wider and still pass through the Panama Canal, which meant that it didn’t have space for a torpedo bulge. Torpedoes were the main offensive weapon used by the Japanese navy against larger surface ships.
The North Carolina had room for a five-compartment torpedo defense system with a traditional torpedo bulge. This was likely 10-20% more effective overall. The South Dakota, with its internal belt and cramped machinery spaces, had a less effective torpedo defense system - narrower, with no bulge and only four compartments. Torpedoes were the single most dangerous threat to battleships in World War II. The USS North Carolina was one of the few battleships to remain in action after being struck by a torpedo.
When the US Navy was designing the Montana class based on the lessons learned in the early stages of the war, they chose to go back to an external belt and a torpedo bulge like the North Carolina class, not the internal belt and compact torpedo defense system of the South Dakota class.
Anti-aircraft power
While in service in World War II, all battleships that didn’t sink were rapidly refitted with more and more anti-aircraft firepower in additional light guns. For United States battleships, adding more light anti-aircraft weapons meant adding quadruple-mount 40mm Bofors guns and cramming 20mm guns in everywhere they could be fit. For older US battleships, it also meant replacing older 5” guns with the new 5”/38 guns, which were very effective in an anti-aircraft role.
The USS North Carolina ended the war with fifteen Bofors quad mounts, because that’s how many could be used effectively from her decks. The USS Alabama, BB-60, never installed more than twelve - because experience on the USS Indiana (BB-58) and USS Massachusetts (BB-59) proved that additional mounts couldn’t be effectively used.
The USS South Dakota itself (BB-57) carried more 40mm quad mounts, but only had sixteen 5”/38 guns instead of twenty. After installing and removing some ineffective mounts, she ended the war with seventeen Bofors quad mounts. (Some fact sheets erroneously describe the whole class as having ten double 5”/38 turrets plus nineteen quad 40mm turrets.)
In other words, the North Carolina class could fit about 25% more light anti-aircraft firepower. Even after accounting for the fact that the heavier 5”/38 guns were very effective in an anti-aircraft role, having more guns (and clearer fields of fire for its more widely spaced 5”/38 guns) meant the North Carolina class had about a 10% advantage in overall anti-aircraft firepower.
The hard price of armor
By the end of WWII, the North Carolina class had shown the following clear quantifiable advantages over the South Dakota class:
10% more anti-aircraft firepower with 25% more light anti-aircraft guns and clearer fields of fire.
25% more layers in its torpedo defense system as well as additional breadth, likely at least 10% more effective.
A slightly higher top speed with a smaller and less powerful engine.
The South Dakota traded all of this away for 10% thicker armor in the areas protecting key components of the ship. Both ships used “all or nothing” protection schemes that left other components similarly unprotected, and the North Carolina class had armor that provided adequate protection against the 14” guns used on most Japanese battleships.
What this meant was that in theory, the South Dakota class was better protected in a gun duel with a peer battleship, but more vulnerable to Japanese aircraft, submarines, cruisers, destroyers, and torpedo boats, each of which was a more numerous threat. However, in practice, it’s not clear that the South Dakota class had more staying power in a gun duel with another battleship.
Soft factors
When I say the North Carolina class was leggier, I don’t just mean a bit more hydrodynamic and a tiny bit faster. The South Dakota class was physically more cramped and less comfortable, had a slightly deeper draft making it slightly harder to dock, had an internal armor belt that was more difficult to repair and service, and was generally just a little bit more annoying to keep in service.
The North Carolina class was leggier on the logistical scale. This wasn’t just an issue for the battleship itself; the battleships operating in the Pacific served as mobile bases, even to the point of fabricating replacement engine parts for smaller ships. While difficult to quantify, morale was important. The North Carolina class was better equipped for extended operations. It was easier to refit and repair.
The US Navy gave serious consideration to converting the North Carolina class ships to aircraft carriers, a plan that had been seriously considered for the Iowa class as well. The shorter and stubbier South Dakota class, on the other hand, would have been much more difficult to re-engineer to the 30+ knot speeds the Navy believed were required for effective aircraft carriers.
Being more difficult to maintain doesn’t just matter on the logistical scale or refits carried decades after being made, though. A duel between two battleships can last for hours, and damage control is critical. If the ship is cramped and more difficult to navigate, it’s harder to conduct proper damage control. If critical and fragile systems are packed closely together, they are more likely to be disabled all at once. Rapid damage control efforts of the crew were critical to keeping the USS North Carolina in action after it was struck by a torpedo.
The duel the USS South Dakota lost
Late at night on November 14th, the USS South Dakota (BB-57) and the USS Washington (BB-56), the classmate of the USS North Carolina, encountered a Japanese task force including one Kongo-class battleship, the Kirishima. At this point, the Washington had been in service for eighteen months, and the South Dakota had been in the field for eight months. This was not the first battle for either ship, and two guns of the South Dakota’s main battery were out of action from bomb damage.
The two American battleships were escorted by four destroyers, all of which were either disabled or destroyed before the Kirishima engaged. During this first part of the battle, the South Dakota experienced major electrical failures and set two of her own floatplanes on fire.
Most accounts of this battle focus on how the USS Washington’s highly accurate shellfire sank the Kirishima. Washington fired 117 rounds from her main battery, 75 of those at Kirishima, most likely hitting the enemy battleship with 20. Analysis indicates she was solely responsible for sinking the Kirishima. Very few battleships can be given credit for sinking another battleship, much less sole credit, and this puts the Washington in elite company.
The South Dakota scored one likely hit (on the destroyer Ayanami) out of 115 main battery rounds fired. The Kirishima reportedly fired 117 rounds from its main battery, likely striking the South Dakota with 6. The Kirishima was equipped with eight 14”/45 guns and a secondary battery of 6” guns. The South Dakota’s armor performed within its design specifications, and the South Dakota’s critical structural components were fine.
However, numerous “softer” components of the ship, including radar, fire control directors, and ammunition storage for anti-aircraft guns, were severely damaged. All radio antennas were destroyed, leaving the South Dakota unable to communicate with other American ships. Multiple fires were set, and weren’t brought fully under control until nearly an hour after the South Dakota disengaged. The South Dakota was rendered ineffective and nearly blind; and without the presence of the Washington, would likely have been put permanently out of action by continued shellfire and torpedoes.
Summary
When the US Navy authorized the South Dakota class, they focused narrowly on one perceived deficiency of the North Carolina class: Armor that they felt would likely be defeated by peer battleships with 16” guns. Working within treaty restrictions to improve the ability of the South Dakota to win duels with peer battleships, though, made the class more vulnerable to damage from many other threats and more difficult to service and maintain. The “upgrade” was worse than the original leggier design of the North Carolina class.
In service, the two North Carolina class ships earned 28 battle stars, with the USS North Carolina becoming the most decorated American battleship of World War II. The four ships of the South Dakota class, combined, earned 42 battle stars - only three times as many. None of these six ships ever dueled either of the two Japanese Nagato class battleships, which had the 16” guns the South Dakota’s improved armor scheme was designed to counter. All were targeted by Japanese torpedoes and aircraft, and they needed every inch of their metaphorical legs trying to keep up with fast-moving aircraft carriers.