Design and construction
Portland was the lead ship of the third class of "treaty cruisers" to be constructed by the United States Navy following the Washington Naval Treaty of 1922, following the two vessels of the Pensacola class ordered in 1926 and the six vessels of the Northampton class ordered in 1927. Ordered for the U.S. Navy in Fiscal Year 1930. Portland was originally designated as a light cruiser, because of her thin armor, and given the hull classification symbol CL-33. She was reclassified a heavy cruiser, because of her 8-inch guns, with the symbol CA-33 on 1 July 1931, in accordance with the London Naval Treaty.
Portland was designed for a standard displacement of 10,258 long tons (10,423 t), and a full-load displacement of 12,755 long tons (12,960 t). However, Portland only displaced 9,800 long tons (10,000 t) when completed. In 1943, a light tripod was added forward of the second funnel on the ship, and a prominent fire-control director was installed aft.
Her four Parsons GT geared turbines each drove a propeller shaft using steam provided by eight Yarrow boilers. Portland's power plant generated 107,000 shaft horsepower (80,000 kW) and she had a designed maximum speed of 32 knots (59 km/h; 37 mph). The ship reached, however, 32.7 knots (60.6 km/h; 37.6 mph) on sea trials. She rolled badly until fitted with bilge keels. Portland was designed for a range of 10,000 nautical miles (19,000 km; 12,000 mi) at 15 knots (28 km/h; 17 mph).
The ship was armed with a main battery of nine Mark 9 8"/55 caliber guns arrayed in three triple mounts, a superfiring pair forward and one aft. She was armed with eight 5"/25 caliber guns for anti-aircraft defense, and she also had two QF 3 pounder Hotchkiss saluting guns. In 1945, her anti-aircraft defenses were upgraded, receiving twenty four Bofors 40 mm guns which were arranged in four quad mounts and four twin mounts. Portland was also upgraded with seventeen Oerlikon 20 mm cannons.
She was originally designed with 1 inch (25 mm) of armor for deck and side protection, but during construction her armor was increased. As completed, the ship was protected with 3.25 inches (83 mm) of belt armor which increased to 5 inches (130 mm) around the magazines. Her armor was between 2 inches (51 mm) and 5.75 inches (146 mm) thick on the transverse bulkheads, while armor on her main deck was 2.5 inches (64 mm) thick. Armor on her barbettes was 1.5 inches (38 mm) thick, armor on her gunhouses was 2.5 inches (64 mm) thick, and armor on her conning tower was 1.25 inches (32 mm) thick.
Additionally, the Portland-class cruisers were designed with space to be outfitted as fleet flagships, with accommodations for an Admiral and his staff to operate. The class also featured two aircraft catapult amidships, and she could carry four aircraft which were stored in a hangar. Her total crew complement varied, with a regular designed crew complement of 848, a wartime complement of 952, and a complement 1,229 when the cruiser was operating as a fleet flagship.
Portland was laid down by Bethlehem Steel at its Quincy Shipyard on 17 February 1930. The machinery was provided by the builders. Portland was launched on 21 May 1932 and commissioned on 23 February 1933. She was the first ship named for the city of Portland, Maine, and sponsored by the daughter of Ralph D. Brooks of Portland, and with Captain Herbert F. Leary as her first commander. Her sailors would later nickname her "Sweet Pea."