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 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.

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.

The US Navy Bureau of Construction and Repair's (C&R) first sketch was unsatisfactory; their lengthy design of 625 feet (191 m) and 30,000 long tons (30,481 t) actually had less armor than the Nevadas, with a 12.5-inch (320 mm) belt.

[5] 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.

In April, the General Board chose the seventh design, which satisfied all of their requirements, albeit on the largest displacement, 31,300 long tons (31,800 t).

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.

[8] 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.

)[19]Tillman's proposal was, in his own words, treated as a "joke"; the Advocate of Peace stated that "it is nearly impossible to read this ... without having an inextinguishable bout of laughter.

The first design submitted by C&R was a severely enlarged Nevada, or a 38,000 long tons (39,000 t) ship with twelve 14-inch guns, 17 to 9 inches (430 to 230 mm) belt armor, and a maximum speed of 23 knots (43 km/h; 26 mph) for a price of $19.5 million.

Arizona was authorized on 4 March 1913, but to avoid a lengthy delay between the two, the ship was ordered much more quickly, on 24 June, by giving the contract to a navy-owned shipyard.

[25] The as-yet unnamed Arizona was laid down on the morning of 16 March 1914 with Assistant Secretary of the Navy Franklin Delano Roosevelt in attendance,[26] and the builders intended to set a world-record ten months between keel-laying and launch,[27] These ambitious goals—Pennsylvania's anticipated completion date was a full two months earlier than the American record—were set by Navy Secretary Josephus Daniels, who wanted the United States to compete with British and German achievements.

Pennsylvania escorted the American President Woodrow Wilson's transport, George Washington, across the Atlantic for the Paris Peace Conference in 1919.

Aside from that, Pennsylvania and Arizona received similar treatment: the elevation of the main batteries was increased to 30°, new fire control systems on tripod masts were added, the secondary armament and directors were replaced and overhauled, eight 5-inch/25 caliber anti-aircraft guns (four per side) were mounted on the weather deck which was above the secondary anti-ship 5-inch gun battery, and their bridges were enlarged to hold elevated anti-aircraft directors.

Two years later, on 7 December 1941, the Japanese attack on Pearl Harbor led to the sinking of Arizona with a direct hit from a 800 kilogram (1,757 lb) bomb to her forward ammunition magazines, causing a tremendous explosion which killed 1,177 officers and men of the 1,512 that were aboard her that morning.

[43] Pennsylvania came back into service more quickly than many of the other battleships present during the attack; she left on 20 December and was under repair in San Francisco until 30 March 1942.

For the next several months, Pennsylvania was stationed on the United States' West Coast, before being reassigned to Pearl Harbor as the fleet flagship for a short time (August to October).

After another refit in San Francisco, which lasted until February 1943, the ship was sent to assist American forces engaged in the Aleutian Islands Campaign.

[44] For the next year, Pennsylvania provided shore bombardment during the Battles of Makin, Kwajalein, Eniwetok, and Saipan, along with the Palau Islands Campaign.

[45] In 1945, Pennsylvania was sent for another refit in San Francisco, and the guns in her main battery, worn out from the frequent shore bombardments, were replaced by those from Nevada and USS Oklahoma.

After the refit’s completion in July, the ship bombarded Wake Island on 1 August en route to Okinawa, where she was struck by an air-dropped torpedo.

The ship's last action was to fire at a kamikaze on 13 August; she was then towed to Guam beginning on the 18th, where temporary repairs were effected, before being sent to Navy Yard Puget Sound for a more permanent solution.

Pennsylvania made it to Puget Sound on 24 October, albeit not without a great deal of trouble caused by temporary repair work.

[46] With the Japanese surrender on 2 September, the Puget Sound repairs were limited to those necessary to ensure Pennsylvania's delivery to Bikini Atoll for atomic experiments in July 1946.

The old battleship survived the tests, but was decommissioned on 29 August and used for radiological studies prior to being sunk as a target ship on 10 February 1948.