The Pennsylvania class consisted of two super-dreadnought battleships built for the United States Navy just before the First World War. Named and , after the American states of the same names, the two battleships were the United States' second battleship design to adhere to the "all or nothing" armor scheme. They were the newest American capital ships when the United States entered the First World War.
The s represented a marked increase in the United States' dreadnought technology, and the Pennsylvania class was intended to continue this with slight increases in the ships' capabilities, including two additional /45 caliber guns and improved underwater protection. The class was the second standard type battleship class to join the US Navy, along with the preceding Nevada and the succeeding , and classes.
In service, the Pennsylvania class saw limited use in the First World War, as a shortage of fuel oil in the United Kingdom meant that only the coal-burning ships of Battleship Division Nine were sent. Both were sent across the Atlantic to France after the war for the Paris Peace Conference of 1919, and were then transferred to the Pacific Fleet before being significantly modernized from 1929 to 1931. For the remainder of the inter-war period, the ships were used in exercises and fleet problems. Both Pennsylvania and Arizona were present during the Japanese attack on Pearl Harbor, which brought the United States into the Second World War. Arizona was sunk by a massive magazine explosion and was turned into a memorial after the war, while Pennsylvania, in dry dock at the time, received only minor damage. After a refit from October 1942 to February 1943, Pennsylvania went on to serve as a shore bombardment ship for most of the remainder of the war. Pennsylvania was present at the Battle of Surigao Strait, the last battle ever between battleships, but did not engage. Pennsylvania was severely damaged by a torpedo on 12 August 1945, two days before the cessation of hostilities. With minimal repairs, she was used in Operation Crossroads, part of the nuclear testing at Bikini Atoll, before being expended as a target ship in 1948.
Background
The preceding Nevada-class battleships represented a leap forward from previous American battleship technology and from most contemporary foreign designs. They were the first in the world to employ the "all or nothing" armor scheme that characterized every succeeding American battleship. Devised with the knowledge that engagement ranges between battle fleets was growing greater as main battery sizes increased, the system moved away from previous designs that used heavy, medium, and light armor, in favor of using only heavy armor to protect vital areas on the ship. The new system envisioned that, at long ranges, ships would be attacked with only armor-piercing (AP) projectiles, stoppable only by heavy armor. Medium or light armor would only serve to detonate the shells. By removing gun turrets and reducing the overall protected length of the ship, the navy's designers were able to devote the weight savings to the belt, as well as extra deck armor to protect against plunging shells.Friedman, Design and Development, 65–66; Friedman, US Battleships, 101–02.
In issuing desired specifications for the design that would become the Nevada class, the Navy's General Board asked for triple gun turrets, i.e., three guns mounted per turret. They were very unsatisfied with the awkward placement required on classes preceding the Nevadas, which had five and six two-gun turrets—yet moving back to the four two-gun turrets of the would be a significant loss in firepower. Although a triple turret was first proposed in American professional magazines in 1901 and briefly considered for the South Carolinas, it was not even in the experimental stage—the first turret was authorized in 1911 and would not be ready until months after contracts for the new ships would be signed with the shipbuilders. The decision to go ahead with the turret was a calculated gamble, but proved to be a qualified success; the only issue came with shell interference when the center and outside guns were fired simultaneously, which was easily solved by delaying the firing of the center barrel by a small fraction of a second. Moreover, there was a major benefit in weight thanks to the accompanying loss of an armored barbette and turret. These weight savings were applied to the armor protection, making the "all or nothing" concept a reality.Friedman, Design and Development, 134–35; Friedman, US Battleships, 102, 107, 111.
The Nevadas were also the first American battleships to use exclusively oil fuel, which had greater thermal efficiency than firing with coal or coal sprayed with oil. The cumulative effect of the change was measured by the navy as a fifty-five percent increase in steam production per pound of fuel (in a design for an oil-fired version of the ). This would give oil-fired vessels additional range, an important consideration for ships based in the Pacific, but the Navy's Bureau of Construction and Repair (C&R) pointed out what it saw as the unfortunate side effects, including a lower center of gravity, higher metacentric height, and the loss of coal bunkers, which were employed as part of the armor protection. Within a few years oil tanks below the waterline were considered indispensable parts of the underwater armor scheme employed in American dreadnoughts.Friedman, Design and Development, 93–95; Friedman, US Battleships, 102, 104–05.
Design
The General Board's call for a new 1913 fiscal year battleship design was sent in June 1911 with the recent Nevada innovations in mind. They desired a ship with a main battery of twelve 14-inch guns in triple turrets, a secondary battery of twenty-two guns, a speed of , and armor equivalent to that of the Nevadas. The US Navy Bureau of Construction and Repair's (C&R) first sketch was unsatisfactory; their lengthy design of and actually had less armor than the Nevadas, with a belt.Friedman, US Battleships, 113.
The design process was marked by various efforts to meet the General Board's specifications with only a moderate increase in tonnage over the Nevada class. Between January and March 1912, thirteen sketches were prepared for consideration by C&R with reciprocating or turbine engines that traded either speed or metacentric height for armor. Some later designs gave up a half knot of speed to free up about , enough to thicken the belt from and the barbettes to 14 inches. The choice between double or triple turrets was also still an issue, as the Nevada class had not been completed yet. The Bureau of Ordnance was in favor of waiting for test results, rather than risking reverting to two-gun 14-inch turrets or moving up to two-gun 16-inch turrets.Friedman, US Battleships, 113–15.
In March 1912, C&R proposed their seventh, eighth, ninth, and tenth designs to the General Board for approval. The eighth and ninth designs were the ones to give up a half knot of speed, while the tenth was a design with four triple turrets and lighter than the Nevada-class ships. In April, the General Board chose the seventh design, which satisfied all of their requirements, albeit on the largest displacement, . The length was fixed at , the beam at , and the draft at . Steam turbines gave the design and 21 knots, while the main armor belt was 13.5 inches tapering to at the ends. This design was further refined and emerged in a completed state in September. The delay was partially due to tests on the proposed armor, which were completed in June 1912 and resulted in significant alterations to the Pennsylvania-class' underwater protection.Friedman, US Battleships, 114–15.
Specifications
The Pennsylvania-class ships were significantly larger than their predecessors, the Nevada class. They had a waterline length of , an overall length of , a beam of (at the waterline), and a draft of at deep load. This was longer than the older ships. Its designed standard and full load displacements were and , respectively, but they actually displaced standard and at full load, over more than the older ships. The class had a metacentric height of at full load.Friedman, US Battleships, 440.
The ships had four direct drive Parsons steam turbine sets with geared cruising turbines, each of which drove a propeller in diameter.Stillwell, Battleship Arizona, 360. They were powered by twelve Babcock & Wilcox water-tube boilers. The turbines were designed to produce a total of , but only achieved during Pennsylvanias sea trials, when it slightly exceeded its designed speed of . Pennsylvania reached during full-power trials in 1916, and Arizona reached in September 1924.Stillwell, Battleship Arizona, 305; "Trials of Our Latest Dreadnought," Scientific American, 297. The class was designed to normally carry of fuel oil, but had a maximum capacity of . At full capacity, they could steam at a speed of for an estimated ; this could be extended to with a clean bottom. They had four turbo generators.
The Pennsylvania class carried twelve 14-inch/45 caliber guns in triple gun turrets. The guns could not elevate independently and were limited to a maximum elevation of +15° which gave them a maximum range of .Friedman, US Battleships, 135.Wright, "The US Navy's Study of the Loss of the Battleship Arizona," 66, 123, 285. The ships carried 100 shells for each gun. Defense against torpedo boats was provided by twenty-two 5-inch/51 caliber guns mounted in individual casemates in the sides of the hull; these proved vulnerable to sea spray and could not be worked in heavy seas.Friedman, US Battleships, 116, 440. At an elevation of 15°, they had a maximum range of .Campbell, Naval Weapons of World War II, 136. Each gun was provided with 230 rounds of ammunition. The ships mounted four /50 caliber anti-aircraft (AA) guns, although only two were fitted when completed. The other pair were added shortly afterward on top of Turret III.Stillwell, Battleship Arizona, 19. The class also mounted two submerged torpedo tubes and carried 24 Bliss-Leavitt Mark 3 torpedoes for them.
The Pennsylvania-class design continued the all-or-nothing principle of armoring only the most important areas of the battleships, which began in the preceding Nevada class. The waterline armor belt of Krupp armor measured 13.5 inches thick and only covered the class' machinery spaces and magazines. It had a total height of , of which was below the waterline; beginning below the waterline, the belt tapered to its minimum thickness of 8 inches. The transverse bulkheads at each end of the ships ranged from 13 to 8 inches in thickness. The faces of the gun turrets were thick while the sides were thick and the turret roofs were protected by 5 inches of armor. The armor of the barbettes was thick. The conning tower was protected by of armor and had a roof eight inches thick.
The main armor deck was three plates thick with a total thickness of 3 inches; over the steering gear the armor increased to in two plates. Beneath it was the splinter deck that ranged from in thickness.Friedman, US Battleships, 115, 118, 440. The boiler uptakes were protected by a conical mantlet that ranged from in thickness.Stillwell, Battleship Arizona, 359. A 3-inch torpedo bulkhead was placed inboard from the side, and the class was provided with a complete double bottom. Testing in mid-1914 revealed that this system could withstand of TNT.
Authorization and construction