USSConcord in 1943
Class overview
Name	Omaha class
Operators	United States Navy  Soviet Navy
Preceded by	Chester class
Succeeded by	Brooklyn class
Built	1918–1925
In commission	1923–1949
Planned	10
Completed	10
Scrapped	10
General characteristics
Type	Light cruiser
Displacement	7,050long tons (7,163 t) standard, 9,508long tons (9,661 t) full
Length	550 ft (170 m)wl 555 ft 6 in (169.32 m)oa
Beam	55 ft 4 in (16.87 m)
Draft	20 ft 0 in (6.10 m)
Installed power	12 × 265 psi (1,830 kPa)Yarrow boilers 90,000 shp (67,000 kW)
Propulsion	4 ×Westinghouse reduction gearedsteam turbines 4 ×screws
Speed	35 kn (65 km/h; 40 mph)
Endurance	9,000 nmi (17,000 km; 10,000 mi) at 10 kn (19 km/h; 12 mph)
Boats & landing craft carried	2 ×lifeboats
Complement	29 officers 429 enlisted (peace time)
Sensors & processing systems	CXAM-1air-search radar SK-1air-search radar
Armament	2 × dual6"/53 cal guns 8 × single 6"/53 cal guns 2 × single3"/50 cal guns 2 × triple21"torpedo tubes 2 × dual 21" torpedo tubes 224 ×mines
Armor	Belt: 3 in (76 mm) Deck:1+1⁄2 in (38 mm) Conning Tower:1+1⁄2 in Bulkheads:1+1⁄2-3 in
Aircraft carried	2 ×floatplanes
Aviation facilities	2 ×aircraft catapults

TheOmaha-class cruisers were a class oflight cruisers built for theUnited States Navy. They were the oldest class of cruiser still in active service with the Navy at the outbreak ofWorld War II, being an immediate post-World War I design.

Maneuvers conducted in January 1915 made it clear that theUS Atlantic Fleet lacked the fast cruisers necessary to provide information on the enemy's position, deny the enemy information of the fleet's own position, and screen friendly forces. Built to scout for a fleet ofbattleships, theOmaha class featured high speed (35 kn (65 km/h; 40 mph)) for cooperation withdestroyers, and 6-inch (152 mm) guns to fend off any destroyers the enemy might send against them. Displacing 7,050long tons (7,160 t), they were just over 555 ft (169 m) long.^[1]

TheOmaha class was designed specifically in response to theBritishCentaur subclass of theC-classcruiser. Although from a modern viewpoint, a conflict between the US and Great Britain seems implausible, US Navy planners during this time, and up to the mid-1930s, considered Britain to be a formidable rival for power in the Atlantic, and the possibility of armed conflict between the two countries plausible enough to merit appropriate planning measures.

TheOmaha class mounted four smokestacks, a look remarkably similar to theClemson-class destroyers (a camouflage scheme was devised to enhance the resemblance). Their armament showed the slow change fromcasemate-mounted weapons toturret-mounted guns. They carried twelve6 in (150 mm)/53caliber guns, of which four were mounted in two twin turrets, one fore and one aft, and the remaining eight in casemates; four on each side, at the corners of the superstructure. This gave them a broadside of eight guns. Launched in 1920,Omaha (designated C-4 and later CL-4) had a displacement of 7,050 long tons. The cruisers emerged with a distinctly old-fashioned appearance owing to their World War I-type stacked twin casemate-mount cannons and were among the last broadside cruisers designed anywhere.^[2]

Additional torpedo tubes and hydrophone installation was ordered. As a result of the design changes placed on the ship mid-construction, the vessel that entered the water in 1920, was a badly overloaded design that, even at the beginning, had been rather tight. The ships were insufficiently insulated, too hot in the tropics and too cold in the north. Sacrifices in weight savings in the name of increased speed led to severe compromise in the habitability of the ship. While described as a good ship in a seaway, the low freeboard led to frequent water ingestion over the bow and in the torpedo compartments and lower aft casemates. The lightly built hulls leaked, so that sustained high-speed steaming contaminated the oil tanks with sea water.^[3]

A serious flaw in these ships' subdivision was the complete lack of watertight bulkheads anywhere above the main deck or aft on the main deck.^[4]

These drawbacks notwithstanding, the US Navy took some pride in theOmaha class. They featured improved compartmentalization; propulsion machinery was laid out on the unit system, with alternating groups of boiler rooms and engine rooms, to prevent immobilization by a single torpedo hit. Magazines were the first to be placed on centerline, below the waterline. These were also the first U.S. Navy cruisers designed after the switch from coal to oil-fired boilers.

Originally designed to serve asscouts, they served throughout the interwar period asleaders of fleet flotillas, helping them resist enemy destroyer attack. Tactical scouting became the province of cruiser aircraft, and the distant scouting role was taken over by the new heavy cruisers spawned by theWashington Naval Treaty. Thus, theOmaha class never performed their designed function. They were relegated to the fleet-screening role, where their high speed and great volume of fire were most appreciated.^[5]

During their careers theOmahas went through several armament changes. Some of these changes were to save weight, while others were to increase their AA armament. On 8 September 1926, theChief of Naval Operations,AdmiralEdward W. Eberle, along with the Commanders in Chief of theUnited States Fleet andBattle Fleet, and their subordinate commanding officers, theSecretary of the Navy,Curtis D. Wilbur, ordered that all mines and the tracks for laying the mines be removed from all of theOmaha-class cruisers, as the working conditions had been found to be very "wet". In 1933–1934, their 3-inch AA guns were increased from two to eight, all mounted in the ship's waist.^[6] The lower torpedo tube mounts, which had also proved to be very wet, were removed and the openings plated over before the start of World War II. After 1939, the lower aft 6-inch guns were removed from most of theOmahas and the casemates plated over for the same reason as the lower torpedo mounts. The ships' AA armament was first augmented by three quadruple1.1-inch (28 mm)/75 gun mounts by early 1942, however, these did not prove reliable and were replaced by twin40-millimeter (1.57 in) Bofors guns later in the war. At about the same time they also received20-millimeter (0.79 in) Oerlikon cannons.^[7]

BothDetroit andRaleigh were atPearl Harbor during the Japanese surprise attack, withRaleigh being torpedoed.Detroit, along withSt. Louis andPhoenix, were the only large ships to get out of the harbor during the attack.

Most ships of theOmaha class spent the war deployed to secondary theaters and in less vital tasks than those assigned to more recently built cruisers. TheOmaha class were sent to places where their significant armament and speed might be useful if called upon, but where their age and limited abilities were less likely to be tested. These secondary destinations included patrols off the east and west coasts of South America, convoy escort in the South Pacific far from the front lines of battle, patrols and shore bombardment along the distant and frigidAleutians andKuril Islands chains, and bombardment duty in theinvasion of Southern France when naval resistance was expected to be minimal.Marblehead participated in early war actions around theDutch East Indies (most notably, theBattle of Makassar Strait), andRichmond would engage in theBattle of the Komandorski Islands. The most significant action that any of the ships of the class would see during the war wasDetroit during her time in the pacific theater.Detroit would see action inThe Battle of Iwo Jima andThe Invasion of Okinawa being assigned to the fifth fleet and serving as the flag ship of the Logistics Support Group (TF 50.8).

None of the ships were wartime losses.Raleigh's torpedo damage at Pearl Harbor andMarblehead's damage at Makassar Strait were the only significant wartime combat damage suffered by the class.

The ships of the class were considered obsolete as the war ended, and were decommissioned and scrapped within seven months of thesurrender of Japan (with the exception ofMilwaukee, which had been loaned to the Soviet Navy, and was scrapped when returned to US Navy control in 1949).

The following ships of the class were constructed.^[8]

Two otherOmaha versions were also designed. The first, intended to function as a monitor, had two 14-inch guns in 2 single turrets, while the other design had four 8-inch guns in two twin turrets. The second design eventually evolved into thePensacola-class cruiser. Furthermore, in 1928 after seeing the successes ofLangley a proposed carrier alternative was designed, featuring none of her 2 × twin 6 in/53 caliber turrets, and only including 4 of the original single 6 in/53 caliber turrets.^{[citation needed]}

• List of cruisers of the United States Navy

• Terzibashitsch, Stefan (1988).Cruisers of the US Navy 1922–1962.Naval Institute Press.ISBN 0-87021-974-X.
• Watts, John W. (7 April 2017)."Omaha II (CL-4)".Dictionary of American Naval Fighting Ships.Naval History and Heritage Command. Retrieved4 November 2019. This article incorporates text from this source, which is in thepublic domain.

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