They were designed to the same treaty standard displacement limit of 35,000 long tons (35,600 t) as the preceding North Carolina class and had the same main battery of nine 16"/45 caliber Mark 6 guns in three-gun turrets, but were more compact and better protected.

[a] A number of deficiencies in the preceding North Carolinas were to be fixed in the South Dakotas; these included insufficient underwater protection and turbine engines not of the most recent technology.

The belt armor was a much more intractable problem; the 16-inch gun could penetrate 13.5 inches (340 mm) of plate, the thickest in an American battleship at the time, even at 25,000 yd (23,000 m).

However, the effectiveness of the upper portion of the belt was degraded at longer ranges, because plunging fire would strike it at an angle closer to the perpendicular, increasing their ability to penetrate the armor.

[4] Because the belt was internal, it provided the opportunity to extend it to the inner portion of the double bottom, which gave the ship better underwater protection than the North Carolinas.

However, in late 1936, cryptanalysts deciphered radio traffic from the Japanese navy which revealed that the battleship Nagato was capable of speeds in excess of 26 knots (48 km/h).

[6] To counter this, it was determined a top speed of 25.8–26.2 kn (47.8–48.5 km/h; 29.7–30.2 mph) was possible if the power plant from North Carolina could be reduced in size enough to fit in the tighter hull of South Dakota.

Arguments arose, frequently over the issue of speed; the Commander in Chief, United States Fleet (CINCUS) refused to allow the new ship to drop below 25 knots (46 km/h; 29 mph), the Battle Force argued at least 27 knots (50 km/h; 31 mph) was necessary to maintain homogeneity in the line of battle, and the president of the War College maintained a fast ship was optimal, but the navy would continue to operate the older 21 knots (39 km/h; 24 mph) battleships until the 1950s and so a higher speed was not strictly necessary—though, crucially, it would mean the class would have been too slow to act in what would emerge as the most critical role for battleships, as escorts for fast carrier task forces.

[10] Despite the compromises made, naval historians William Garzke and Robert Dulin would later argue that the South Dakota-class ships were the best treaty battleships ever built.

As Friedman has written: For half a century prior to laying the Iowa class down, the U.S. Navy had consistently advocated armor and firepower at the expense of speed.

[16] The South Dakota–class battleships carried a main battery of nine 16 inches (406 mm)/45 caliber Mark 6 guns in three three-gun turrets, identical to the North Carolina-class.

The displacement of the vessels gradually increased over World War II, mainly due to additional light anti-aircraft gun placements and greater fuel oil carriage to refuel smaller escorts.

It was hoped that extending the armor belt to the triple bottom as one of the torpedo bulkheads can help increase the protection of the system compared to the one used by the previous North Carolina-class.

However, caisson tests in 1939 indicated that the South Dakota system was less effective due to the rigidity of the armor belt causing force of the detonation to significantly displace the final holding bulkhead inwards despite remaining watertight.

In August–September, the battleship voyaged from the Atlantic to the Pacific through the Panama Canal; she struck a coral reef soon after arriving in the Tonga Islands and had to sail to the Pearl Harbor Navy Yard for repairs, which took about a month.

[31] Partial repairs courtesy of Prometheus' crew allowed South Dakota to sail for New York; after the ship's arrival on 18 December 1942, she was given an overhaul and the battle damage was completely fixed.

Departing the yard on 25 February 1943, South Dakota underwent sea trials before escorting Ranger in North Atlantic operations until mid-April, when she joined the British Home Fleet.

The day of 29 January 1944 saw the ship bombard Roi-Namur before she moved away to protect the carriers assigned to provide air support for multiple amphibious assaults on islands within Kwajalein Atoll.

The battleship took part in the so-called "Marianas Turkey Shoot", where more than 300 attacking Japanese aircraft were shot down, though she was hit by a 500-pound bomb on the main deck that killed 24 and wounded 27.

Decommissioned on 31 January 1947, South Dakota remained idle until she was stricken from the Naval Register on 1 June 1962 and sold for scrap to the Lipsett Division of Luria Brothers and Company, Inc. on 25 October.

After shakedown operations, she was sent directly to the Solomon Islands; Indiana arrived off Guadalcanal on 9 November 1942 and replaced her sister South Dakota, which was in need of repairs.

Following the shore bombardments, Indiana joined the task force that had assembled to invade Okinawa; the ship provided ground support fire as well as anti-aircraft defense against the increasing number of Kamikazes that were attacking the invasion fleet.

[40] After a shakedown cruise, the battleship departed Casco Bay, Maine on 24 October 1942 to support the Allied invasion of Africa, Operation Torch, as flagship of the Western Naval Task Force.

[40] The incomplete French battleship Jean Bart, missing one of her quadruple 380 mm/45 caliber gun turrets, was in the harbor, having traveled there in 1940 to escape the German invasion of France.

Returning to carrier protection after the latter bombardment, Massachusetts provided anti-aircraft defense while Allied air attacks were sent against Saipan, Tinian and Guam; she also supported later invasions of the Caroline Islands and Hollandia.

1 July saw the Third Fleet and Massachusetts set course for Japan; the battleship protected carriers while they launched raids on Tokyo, then moved closer to land to hit targets with gunfire.

[41] With the war over, Massachusetts voyaged to the Puget Sound Navy Yard once more for an overhaul; once completed, she left on 28 January 1946 and operated off the California coast before setting course for Hampton Roads via the Panama Canal.

After she arrived on 22 April, Massachusetts was decommissioned on 27 March 1947 and entered the Atlantic Reserve Fleet; she was struck from the Naval Register on 1 June 1962, but not scrapped.

[41] Construction work on Alabama, the fourth and final member of the South Dakota class, began on 1 February 1940 in the Norfolk Navy Yard with the keel laying.

Minor repairs were carried out in Norfolk, after which the big ship returned to Casco Bay to conduct training maneuvers with her sister, South Dakota.