page_title: Pennsylvania-class battleship
section_title: Background
hierarchical_section_title: Pennsylvania-class battleship / Background
context_page_description: The Pennsylvania-class consisted of two super-dreadnought battleships built for the United States Navy just before the First World War. The ships were named Pennsylvania and Arizona, after the American states of the same names. They constituted the United States' second battleship design to adhere to the "all or nothing" armor scheme, and were the newest American capital ships when the United States entered the First World War.
  The Nevada-class battleships 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 14-inch /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 New Mexico, Tennessee and Colorado classes.
  In service, the Pennsylvania class saw limited use in the First World War, as a shortage of oil fuel in the United Kingdom meant that only the coal-burning ships of Battleship Division Nine were sent.
context_section_description: 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.
  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 South Carolina class 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.
  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 New York class). 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.
caption: The Nevada class, represented here by Oklahoma in 1916, were the first American battleship class with triple gun turrets, the "all or nothing" armor concept, oil fuel, and steam turbines with geared cruising turbines (albeit the latter only in Nevada); all of these innovations were continued in the Pennsylvania class.
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