Intended to serve as destroyer flotilla leaders, four Atlanta (CL-51) class light cruisers were authorized during the pre-World War II build-up program. Armed with eight dual 5-inch/38 gun turrets, they had the firepower of three destroyers. In operational use, they served as excellent anti-aircraft platforms, and the surviving ships were reclassified CLAA (anti-aircraft cruisers) in 1949.
This class was intended to replace the 1920s era Omaha class light cruisers. This class was developed to satisfy the need for a light displacement, high speed vessel whose mission was primarily combating large scale attack by aircraft, but which also possessed the ability to perform certain types of cruiser duty. Their initial purpose, contrary to popular belief, was not only that of an anti-aircraft cruiser but that of a small, fast scout cruiser that could operate in conjunction with destroyers on the fringes of the battle line in addition to the defense of the battle line against destroyer and aircraft attack. While they were not designed to "slug it out" with heaver ships, they were well suited to close surface action in bad weather (poor visibility) and to night actions, where their fast firing 5"/38's and eight 21" torpedos could be used to advantage.
In 1935, an experimental modernization was carried out by the Royal Navy on two British cruisers of WWI vintage, Coventry and Curlew. Their 6-inch main armament was removed and replaced by 4-inch antiaircraft weapons, "for use in the Mediterranean as AA escorts." The idea of a specialized AA ship gained surprising traction with the Admiralty (considering how little experience then existed to show how important AA defense was to a fleet). A new 5.25-inch dual purpose gun was being developed for the new King George V class battleships, and a new small cruiser was designed, the Dido class, to mount 5 twin turrets of these on some 6850 tons full load displacement.
These little ships had 62,000 SHP in a 4-screw power plant, good for 32-plus knots top speed and 4240 miles of range at 16 knots. They were adapted from a more conventional light cruiser design, the Arethusa class. Arethusas were successful as flotilla leaders. Didos were ordered in 1939 and 16 were produced; however, production of the ships outstripped production of the 5.25-inch guns, and some were commissioned with only 4 turrets while others had a turret removed later.
The American version of the antiaircraft cruiser is the Atlanta (CL 51) class. While its armament resembled the Dido's in photos with three twin turrets forward of the bridge, the actual layout was much different with a total of 8 dual purpose, 5inch/38 twin turrets. The propulsion plant was also much different with twin screw, 75,000 SHP for a similar top speed of 32.5 knots. Both ships were adequately armored – Atlanta had a 3.75-inch belt and 1.25-inch deck, with both being part of the hull girder; she was larger at 8340 tons full load.
Perhaps coincidentally, one of the intended functions of the CL 51 class was to replace aging Omaha class flotilla leaders for use in destroyer warfare. A flotilla leader protects destroyers against enemy surface and air attack while the destroyers carry out a torpedo attack against enemy capital ships. The type, sometimes called a destroyer leader, originated with HMS Swift in 1907. High speed is usual in flotilla leaders, and Atlanta was less outstanding than the Omaha's had been in this respect. However, her ability to protect against air attack was excellent. Unlike most US cruisers of the period she was equipped with torpedo tubes and depth charges, reflecting her destroyer-like mission. But, Atlantas were also intended as close screens for the battle line, protecting the capital ships against destroyer attack.
The design consisted of many novel features, including the provision of an inner bottom extending to the second deck and following the contour of the outer shell. The side armor was of watertight reverted construction forming part of the watertight envelope of the hull. Armor protection was moderate, due to the weight limitation dictated by speed requirements, and consisted of side armor in way of the machinery spaces, bulkheads enclosing magazines, conning tower and steering engine room, with lighter protection on decks and on the boundaries off other vital areas.
The propelling machinery was of improved design based on experience gained in the operation of destroyer machinery. Manufactured by Westinghouse Electric Corporation, each set of turbines consisted of one cruising, one high pressure and one double flow low pressure. The cruising turbine connected to the forward end of the high-pressure turbine rotor shaft through a single reduction gear.
In common with many other cruisers, the Atlantas were sometimes used for different functions from those for which they were designed. As a result, two of them were sunk by Japanese cruisers and destroyers while formed up in a battle line of larger US cruisers on 13 November, 1942. The class was most successful as part of the AAW screen around fast carriers, foreshadowing the function of later DL and DLG designs.
During World War II a modification was ordered in which the torpedo tubes and two 5-inch turrets would be replaced by 5 quad and 4 twin 40mm AA guns but this was never completed.
CL-51 and 52 were assigned to Federal Shipbuilding, Kearny NJ. These were laid down Apr-May 1940 and commissioned Dec 1941 and Feb 1942, respectively. Atlanta (CL-51) and Juneau (CL-52) were sunk in a naval battle off Guadalcanal 13 Nov 1942.
CL-53 and 54 were assigned to Bethlehem Shipbuilding, Quincy MA. Laid down in March and May 1940, these joined the fleet Jan-Feb 1942 - both survived the war to decommission in late 1946 and were scrapped 1960-62.
Three follow-on ships (Juneau Class) were commissioned in 1946 and were distinguished from the Atlanta Class by a reduction of the superstructure height by one level, a reduction in the distance between the stacks, and a substantial increase in the antiaircraft batteries. This class had an array of various types of radar antennae installed on the fore and main masts.
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