While the successful fielding of the Omaha Class cruisers gave the US a slight advantage against the Centaur class cruisers, an additional threat to US Navy scout cruiser superiority loomed across the Atlantic which outmatched the Omaha's capabilities. The British Hawkins Class cruisers (1916) boasted seven 7.5-in/45 guns at a displacement of 9,750 tons at a sprint speed of 30 knots. The Hawkins was designed by the British to hunt down German commerce raiders, and had been given an unusually long-range weapon that might enable them to cripple such raiders before they could flee. This counter-raider had the unintended effect of upgrading foreign designs, partly because of its potential as a raider.
For the US Navy, the Hawkins became the standard for cruisers designed for independent operations, with planners demanding six 8-inch guns and a speed of 32.5 knots to counter the Hawkins capabilities. The designs produced by the US Navy which were formulated in response to the Hawkins Class would eventually lead to the USS Pensacola, the first of the so called "Treaty cruisers."
If the General Board had strongly favored cruisers before 1922, the Washington Treaty greatly increased its interest in them. In effect the Treaty turned the 8-inch gun cruiser into a kind of junior capital ship. The old scouting role was, if anything, more important in the new kind of Pacific war the navy was then planning than it had been in the Atlantic. Perhaps as importantly, the prospect of losing a single capital ship out of the reduced number surviving under the Treaty would deter a commander from releasing single ships for such roles as convoy escort and shore bombardment. In WWI there had been many obsolete battleships and armored cruisers available for even the riskiest assignments, but they had been wiped out at the conference table. To fill their place, heavy cruisers, their numbers unlimited under the Treaty, would be required.
The General Board had evaluated a number of scout cruiser designs leading up to the Treaty limitations, and continued to evaluate alternatives up to 1924 with the authorization of the Pensacola. The General Board concluded that designs split into two categories depending on what function a cruiser would serve: protecting or destroying merchant ships, or operating with the fleet. Ships in the former role required a speed of 32 to 34 knots, in the latter, 27 to 32 knots. Although opinions on guns and protection differed widely, the Board did agree that aircraft were secondary.
By December 1924 there was enough evidence of foreign willingness to begin a cruiser-building race that Congress authorized eight new cruisers, the Pensacolas (CA 24-25) and the Northamptons (CA 26-31). Two Pensacola (CL-24) class light cruisers were authorized in FY1925. These were the first of the US Navy's Washington Naval Treaty cruisers and the first of the modern cruisers to mount the 8-inch gun designed to match the firepower of Japanese cruisers. The treaty defined cruisers as ships of up to 10,000 tons, and being either "light" with guns no larger than 6 inches, or "heavy" with guns no larger than 8 inches.
The gun arrangement was much like that in the Nevada class though with heavier triple turrets in the superfiring position fore and aft. This would lead to top-weight problems later in their service life when AA armament was added during World War Two. The 6" gun was well liked with the pedestal mounts yielding rapid fire. Its maximum effective range was far less than an 8" gun. The 8" gun was not particularly well liked. It was mounted in the first battleships as the largest available rapid fire gun and the same twin mount was installed in the early cruisers. While the new 8" gun had an effective range over the horizon, it only fired at 3 rounds per minute.
PENSACOLA, like the fast BBs of WWII, favored speed and firepower over protection. These cruisers were very lightly armored by cruiser standards, barely capable of withstanding 5-inch gunfire -- they were commonly referred to as "treaty tinclads".
The great irony was that, after the designs had been largely determined by the need to stay barely within Treaty limits, the ships came out grossly underweight, even after last-minute changes. The full load delivery displacement of 10,666 tons for the Salt Lake City was a full 900 tons underweight. As a result, the both classes had an excessive metacentric height. The roll was, therefore, both short and deep which caused a disconcerting motion. Very heavy snap rolling could even break the topmast, which was essential for long-range radio at this time. This happened to the Salt Lake City when she was en route from New York to Guantanamo early in 1931.
Anti-rolling tanks were installed experimentally in the Pensacola and the Northampton. The tanks were not interconnected, rather, the tank on each side was open to the sea, with a vent pipe. There were also complaints of weak sternposts and excessive vibration aft at high speed, presumably due to weight savings in the hull structure and cured by structural stiffening. The ships seemed light, with serious damage inflicted on the hull of the ship when the three guns of a turret were fired together.
The 8-inch gun cruisers brought a new capability to the fleet when they entered the service. They replaced the elderly battleships of the Scouting Force and served not merely as scouts but, perhaps much more importantly, as escorts for the new fast carriers in independent task force operations.
The first of the Pensacola Class cruisers launched was the USS Salt Lake City (CA 25) on January 23, 1929, with a design displacement of 11,568 tons. Salt Lake City (CL-25) commissioned in 1929 and Pensacola (CL-24) in 1930. The London Treaty of 1930 subdivided cruisers into class A Heavy Cruisers (CA) with guns of over 6.1 inches calibre and type B Light Cruisers (CL), those with guns of 6.1 inches of less. In July 1931, the US Navy redesignated its 8-inch gun cruisers as heavy cruisers and they became CA-24 and CA-25.
Initially armed with sixteen 1.1-inch AA guns, these were replaced with increasing numbers of 20mm and 40mm AA mounts during the war. The torpedo mounts had been removed prior to 1941.
A treaty ship laid down in 1927, by 1943 Salt Lake City was the oldest heavy cruiser the U.S. has. So bare of streamlined beauty was her ungainly silhouette that Time Correspondent Bob Casey (Torpedo Junction) fondly fastened the nickname "Swayback Maru" on her when the censors would not let him reveal her real name. Because she never got hit hard enough to be sent home for repairs, she never got much publicity. But by March 1943 many a high-ranking Navy man was willing to concede that on performance the Salt Lake City was the No. 1 U.S. cruiser of the war. The Salt Lake City had probably been in more engagements than any other American warship. Jap communiques have "sunk" her twice and left her burning once.
Modifications for Operation Magic Carpet, following World War Two included the removal of four single 5-inch gun mounts, two quad 40mm mounts and four twin 20mm mounts.
Both ships were utilized as targets in the July 1946 Bikini Atoll atomic tests and subsequently scuttled in 1948.
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