Pensacola Class Cruisers

The two Pensacola class heavy cruisers were the first American heavy cruisers built after the First World War and were restricted by the terms of the 1921 Washington Naval Treaty.

The Pensacola class ships marked a clear break with pervious American cruisers. The pre-war Chester class had been much lighter ships, armed with two 5in and six 3in guns, all carried in the open. The first post-war class, the Omaha class light cruisers, were quite old fashioned ships, with half of their 6in guns carried in casemates mounted on the sides of the superstructure. During the First World War the US Navy came in close contact with the Royal Navy. The wartime Cavendish or Hawkins class cruisers particularly impressed. They had around the same displacement as the eventual Pensacola class ships, and carried seven 7.5in guns, five on the centre line (three aft and two forward) and one each on each side. They could thus use six of their seven guns in a broadside.

USS Pensacola (CA-24)
at Mare Island,
29 June 1945

The US Navy decided that any cruisers built after the First World War would have to be superior to the Hawkins class. They also wanted cruisers with a large radius of operation in case of conflict with Japan. A wide range of cruiser designs were developed in the early 1920s, ranging from 5,000 to 10,000 tons and armed with 5in, 6in or 8in guns. While this was going on the Omaha class ships, armed with 6in guns, were under construction. The 1921 Washington Naval Treaty also played a major part in the eventual design, imposing a size limit of 10,000 tons and 8in guns on any new cruisers.

The basic design of the Pensacola ships was in place by November 1923 and the final sketch design was completed in March 1925. The new ships had two funnels with a fairly wide gap between them. They had superstructures fore and aft, with large mainmasts and foremasts. Power was provided by 4 shaft Parsons Turbines with eight boilers in two boiler rooms, arranged on the unit principle with the turbine rooms between the boiler rooms.

The Pensacola class ships were the first American cruisers to carry all of their main guns in superfiring turrets carried on the centre line, the layout that was used for the vast majority of Second World War cruisers. They were armed with ten 8in/55 guns, carried in four turrets. The fore and aft turrets carried two guns, the higher inboard turrets carried three each. This allowed the designers to give the ship very fine lines. Secondary armament was provided by four dual purpose 5in guns carried in single mountings just behind the rear funnel, two on each side of the ship.

They were built with six 21in torpedo tubes in two banks of three, but these were removed before the outbreak of the Second World War. By then they had also had four 5in/25 anti-aircraft guns mounted by the forward superstructure

Anti-aircraft armament changed repeated during the two ships service life. At first they only carried .50in calibre Browning M2 machine guns. In November 1941 they received two quad 1.1in Mark VI machine gun mountings (nicknamed the Chicago Piano). In 1942 the .50 machine guns were replaced with 20mm Oerlikon cannon, starting with eight single mountings as well as two more quad 1.1in mountings.

In 1943 quad 40mm Bofors cannons replaced the 1.1in guns and the number of 20mm guns was increased. By 1944 the official mounting was six quad 40mm Bofors mountings and twenty or twenty one 20mm guns. In 1945 the Salt Lake Cityhad six quad 40mm mountings and nineteen single 20mm cannon. After a refit in the summer of 1945 the Pensacolahad seven quad 40mm mountings and nine twin 20mm mountings.

Radar on USS Salt Lake City (CA-25), 10 May 1943

Aircraft were seen as essential for cruiser operations in the 1920s. The Pensacola class cruisers could carry four aircraft which were stored in the open, and had two catapults and a single crane. They carried Vought O2U Corsairs, OS2U Kingfishers or Curtiss SOC Seagulls during their service careers.

The ships were lightly armoured for heavy cruisers. They had a 1in armoured deck, with a belt that varied from 2.5in to 4in. The thicker belt protected the magazines. The turret barbettes were very thinly armoured with .75in armour. The turrets had 2.5in of armour on the face, thinner armour elsewhere.

There was actually plenty of spare weight within the 10,000t limit for extra armour. The theory was that the limited armour would be effective against 5in destroyer guns. They would outrange 6in cruisers and any engagement with another 8in cruiser would take place at such short distances that no effective armour could be carried. While the ships were under construction it was realised that director fire control units could be installed, and so the 8in guns would be effective at much longer ranges than expected. The belt armour was later calculated to be effective against 5.1in fire over 8,000 yards, but vulnerable to 8in/50 shells at up to 24,000 yards and the deck armour over the magazines at 16,000 yards.

Their thin armour meant they became known as 'tin clad' cruisers. The next heavy cruiser class, the Northampton class and Portland class cruisers shared this limited protection but the New Orleans class of the early 1930s saw the first attempt to increase armour.

The impact of the treaty limits can be seen in the Pensacola class. The Cleveland class light cruisers, built after the treaty restrictions were lifted, were longer, slightly wider and 2,000t heavier on standard displacement. The Pensacola class were similar in concept to other cruisers of the period - the contemporary British Kent class cursers carried eight 8in guns on a similar displacement but with thicker armour around the ammo spaces and thinner armour elsewhere.

Both members of the class fought extensively during the Pacific War, with Pensacola earning 13 battle stars and Salt Lake City 11. Both survived the war, making the class more fortunate than their successors - three of the six Northampton class ships were sunk, as was one of the two Portland class ships and three of the seven more heavily armoured New Orleans class

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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