Portland Class Heavy Cruisers

The two Portland class heavy cruisers were slightly modified versions of the Northampton class with better protection for the magazines. Originally five were to be built but only two were completed and the rest became the first New Orleans class cruisers, with significantly improved armour.

In 1929 the US Navy adopted an ambitious programme of construction that included fifteen 8in cruisers. Five were to be built under the FY29 budget (CA-32 to CA-36), five in FY30 (CA-37 to CA-41) and five in FY31 (CA-42-46).

The original plan was to build all of the FY29 ships as modified Northampton class cruisers, themselves an improved version of the earlier Pensacola class. When these plans were originally conceived none of the earlier ships had actually been completed. USS Pensacola had been laid down in 1926, and USS Salt Lake City in 1927. Both were launched early in 1929 and Salt Lake City was completed on 11 December 1929. The six Northampton class ships had been laid down in 1928 and the first three would be launched in 1929 but none were complete until 1930. Even at this stage there was concern over their thin armour, but it was only after the earlier ships became to come into service that it became clear that they were around 1,000 tons under their 10,000 ton displacement limit.

Once it was clear just how much extra weight was available there was a great deal of pressure to add extra armour to the new cruisers. At first the Navy insisted that the first batch were too far along to be modified within a punitive cost penalty, but eventually it was decided that the three ships being built in Navy Yards could be modified without any significant cost. CA-32, CA-34 and CA-35 were all completed as the first ships of the New Orleans class.

This left USS Portland (CA-33) and USS Indianapolis (CA-35), both of which were built at private yards. The Navy decided that it would be too expensive to modify these ships, and so they were produced as modified versions of the Northampton class. They were slightly longer, and lacked the bulbous bow of the earlier ships. They were built without the torpedo tubes installed on the earlier cruisers, and with eight 5in guns. The older ships were built with four 5in guns but all gained another four after they were completed. In service they gained 1.1in anti-aircraft guns, which were later replaced with 40mm Bofors guns as well as a large number of 20mm cannon.

Originally the Portland class ships had similar armour to the Northamptons. The magazine side armour was increased to 5in, then when it became clear just how much weight was available increased again to 5 3/4in. The deck armour was also thickened by half an inch.

In 1933 the Navy worked out the immune zones for the Portland class ships. They estimated that the aft magainzes were protected against 8in fire between 12,000 yards and 20,500 yards and the forward magazines between 12,000 and 23,000 yards (at longer range plunging fire would penetrate the top armour). The belt could be penetrated at 24,000 yards, the deck over the engines at 16,000 yards. The thinly armoured turrets could be penetrated all any combat range.

The basic layout was the same as on the Northampton class ships. They were armed with nine 8in guns in three triple turrets, two at the front and one at the rear. They had two funnels, with a hanger for the spotter aircraft built around the rear funnel and two catapults on towers between the funnels. They had four turbine-driven propeller shafts powered by eight Yarrow boilers. Both ships were equipped as flagships.

The two Portland class ships were ready at least a year ahead of the first of the New Orleans class. They were laid down in February 1930 and March 1930, while the first New Orleans class ship wasn't laid down until September 1930. They were launched in November 1931 and May 1932, with the first of the New Orleans following in April 1933. They were completed in November 1932 and February 1933, a full year before USS New Orleans, which was completed on 15 February 1934.

Both the Portland and the Indianapolis fought in the Pacific during the Second World War. The Portland survived the war, but the loss of the Indianapolis was one of the great tragedies of the war. She was used to transport the first atomic bomb to Tinian, but was sunk by the submarine I-58 on her way back from Tinian to Leyte. She wasn't reported missing for several days and so any rescue operation was delayed. Only 316 of the crew of 1,199 were saved.

Displacement (standard)

10,258t

Displacement (loaded)

12,755t

Top Speed

32.5kts

Range

10,000nm at 15kts

Armour – belt

2.25in

 - machinery

0.75in belt
2.5in deck

 - magazines

5.75in belt
2.125in deck

 - barbettes

1.5in

 - gunhouses

2.5in face
2in roof
0.75in side and rear

Length

610ft oa

Armaments

Nine 8in guns (three 3-gun turrests)
Eight 5in/25 guns (eight single positions)
Eight 0.5in guns (eight single positions)
Four aircraft

Crew complement

807 (917 Indianapolis)

Ships in Class

Fate

CA33 USS Portland

Broken up 1959

CA35 USS Indianapolis

Sunk 29 July 1945

US Heavy Cruisers 1941-45: Pre War Classes, Mark Stille. Looks at the 'treaty cruisers' built in the US between the wars, limited by treaty to 10,000 tons and 8in guns. Five classes of treaty cruisers were produced and they played a major role in the fighting during the Second World War, despite the limits imposed on them by the treaty restrictions. [read full review]
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How to cite this article: Rickard, J (26 February 2014), Portland Class Heavy Cruisers , http://www.historyofwar.org/articles/weapons_portland_class_cruisers.html

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