The USS Pennsylvania was the name ship of the Pennsylvania class of battleships. She was one of the least damaged battleships at Pearl Harbor, and remained in service during 1942 before undergoing a refit late in the year. On her return she took part in a series of island invasions, before being badly damaged by a Japanese torpedo in August 1945.
The Pennsylvania was laid down in 1913, launched in 1915 and commissioned in 1916. She was designed to serve as a flagship, and became Flagship of the Atlantic Fleet on 12 October 1916. Despite this she wasn't one of the ships chosen to work with the British Grand Fleet after the American entry into the First World War - she was an oil burner, and only coal burning ships were chosen, to easy the supply situation.
Both Pennsylvania class ships underwent a major refit during the 1920s. Their maximum gun elevation was raised to 30 degrees, increasing their maximum range. Anti-torpedo bulges were installed underwater. An aircraft launching catapult was fitted. New boilers were installed, using machinery ordered for the USS Washington, a newer battleship scrapped under the terms of the Washington Naval Treaty. The secondary guns were removed from the hull and moved up one level into a deckhouse arrangement that contained eight 5in anti-aircraft guns and two 5in single purpose guns. The cage masts were removed and replaced with tripod masts.
The Pennsylvania underwent a wartime refit at Mare Island late in 1942, after serving with the fleet for most of the year after Pearl Harbor. All of the remaining 5in guns were removed and were replaced with sixteen 5in/38 anti-aircraft guns in twin mountings. The rear tripod mast was replaced with a low tower. The two-tiered fire control tops from the cage masts were replaced with a single deck control top for the main guns while two Mk 37 directors were added to control the 5in guns. As with most Second World War aircraft a large number of smaller anti-aircraft guns were installed during the war, and Pennsylvania eventually carried ten quadruple 40mm mountings and twenty seven single and twenty two twin 20mm anti-aircraft guns.
On 7 December 1941 the Pennsylvania was in Drydock No.1 at Pearl Harbor, with the destroyers Cassin and Downes. The Japanese attempted to torpedo the dry dock gates, but failed, and the Pennsylvania was only lightly damaged. One 250kg bomb hit and destroyed a 5in gun, and the forecast was hit by part of the torpedo tube from the Downes. Fifteen men were killed, 14 missing in action and 38 wounded during the action. The missing gun was replaced by one taken from the West Virginia.