Historically, the U.S. Navy chose to neglect cruisers during its early dreadnought era expansion, building almost exclusively battleships and destroyers. This was seen as the only way to achieve a viable fighting fleet within the extremely limited budgets authorized by Congress. When World War I erupted, the Navy ultimately focused on mass production of critically needed destroyers. Although production of cruisers resumed post-war, budgets were miniscule and only a handful of scout cruisers were built prior to the Washington Naval Treaty.
Treaty Cruisers
Treaty cruisers are defined by the Washington Naval Treaty of 1922, which limits cruisers to an armament of up to 8" guns and a standard displacement of up to 10,000 tons.
7"⁄45 Mark 3 Naval Gun
For its treaty cruisers, the alternate U.S. Navy chooses not to simply use the largest-caliber guns permitted. Instead, it accepts a substantial delay in laying down new cruisers to allow the Bureau of Ordnance to test a variety of intermediate caliber naval guns taken from pre-dreadnoughts and armored cruisers which are now being scrapped. BuOrd validates its previous finding that 7" (178mm) is still the largest calibre practical for a rapid-fire naval gun and further concludes that the range disadvantage of a lighter calibre can be counteracted by the adoption of higher-velocity guns in higher-elevation mountings.
The 7"⁄45 Mark 3 gun developed for the treaty cruisers utilizes a semi-automatic vertical sliding-wedge breechblock and semi-fixed ammunition rather than the more common manually operated Welin interrupted screw breechblock and bagged ammunition, enabling it to operate at a rate of 6-7 rounds per minute. It fires 165-pound AP or HE shells at a muzzle velocity of 2,800 FPS, with a maximum elevation of 40 degrees enabling a range of up to 28,000 yards.
Pensacola Class Cruiser (1924)
The Pensacola class is the U.S. Navy’s first treaty cruiser design, officially designated as a new category of “light armored cruiser” rather than as a scout cruiser or protected cruiser. Two ships of this class are authorized in 1924, and after the lead pair successfully completed their service trials, a further two (with minor improvements) are authorized in 1927.
Design
The Pensacolas have a standard displacement of 10,000 tons and measure 575 feet at the waterline with a beam of 65 feet and a draft of 20 feet. In keeping with the independent scouting and skirmishing roles which cruisers are expected to fill, they are built for a high speed of 33 knots and are equipped with two observation floatplanes (initially Vought O2U Corsairs, later Curtiss SOC Seagulls) on a single amidships catapult. The combination of fine lines, a flush deck layout, and a relatively high superstructure unfortunately gives them a pronounced tendency to roll as well as being fairly wet at the bow. However, their lighter armament allows them to be significantly more robust than other nations' 8" treaty cruisers and the Navy judges the class to be generally satisfactory.
(Due to the resources spent on the six large armored cruisers, substantially fewer early treaty cruisers are authorized in this timeline, with only four alternate Pensacolas as opposed to two Pensacola, six Northampton, and two Portland class treaty cruisers. Compared to their historical counterparts, the alternate Pensacolas’ much lighter 7" guns enable substantially better armor protection on treaty tonnage while also greatly reducing the seakeeping and stability issues which forced a reduction in armament to three turrets in the later treaty cruisers.)
Armament
The Pensacolas are armed with a main battery of twelve 7"⁄45 Mark 3 guns in four triple turrets, a secondary battery of eight 5"⁄25 anti-aircraft guns in single open mounts, and a torpedo battery of eight 21-inch tubes in two quadruple mounts.
The main battery is arranged in a 2-A-2 configuration with two turrets on the forward centerline and two turrets on the aft centerline; turrets #1 and #4 are placed at deck level and turrets #2 and #3 are placed two decks above to superfire over them. In U.S. terminology, these are formally "triple mounts" -- triple because all three guns elevate as a single unit, and mounts because there are fixed handling rooms below the gunhouses rather than a rotating stalk and barbette.
The secondary battery is arranged with one mount on each side of the forward deckhouse at level 02, one mount on each side of the aft deckhouse at level 01, and two mounts on each side of the main deck amidships.
Later refits introduce a tertiary battery of automatic anti-aircraft guns throughout the upper superstructure, initially four quad 1.1"⁄75 "Chicago Pianos" and eight twin .50-caliber machine guns, and later a growing number of 40mm Bofors in quad and twin mounts and 20mm Oerlikons on twin and single pedestals.
Minneapolis Class Cruiser (1934)
Post-Treaty Cruisers
Although the Washington Naval Treaty officially remained in effect until 1936, the United States began designing larger cruisers after ongoing negotiations for a renewed treaty broke down in 1928.
(Historically, the United States started a substantial naval expansion in the post-Treaty years, constructing an additional twenty-one heavy cruisers (plus fifteen more which were cancelled) and thirty-eight light cruisers (plus nine converted into light carriers and fourteen cancelled).
St. Paul Class Cruiser (1937)
The Saint Paul class cruisers are the U.S. Navy’s first post-treaty light cruisers, closely based on the preceding Minnesota class but substantially enlarged to accommodate a fifth main battery turret and two additional secondary battery turrets. Congress authorizes four in 1937, four in 1938, four in 1939, twelve in 1940, eighteen in 1941, and eighteen in 1942 for a total of sixty, the largest class of cruisers ever ordered. In 1941, six of the 1940 order under construction are urgently diverted as Cerritos-class light carriers, followed by a further four of the 1941 order.
The St. Pauls are the backbone of the American cruiser fleet throughout World War II, with roughly half of those produced being converted into post-war guided missile cruisers which serve into the 1980s.
Design
The Saint Pauls have a standard displacement of 15,000 tons and a full load displacement of roughly 18,000 tons. They measure 700 feet long with a beam of 70 feet and a draft of 25 feet.
Armament
The St. Pauls are armed with a main battery of twelve 7"⁄45 Mark 4 guns in three four-gun turrets and a secondary battery of twelve 5"⁄38 Mark 12 dual purpose guns in six twin turrets. They are the first cruisers in service to be built from the start with radar fire control. Tertiary armament consists of four 1.1"⁄75 anti-aircraft autocannons in "Chicago Piano" quad mounts.
The main battery is arranged in a 3-A-0 configuration with all three turrets in a semi-superfiring trio; turret #1 is at deck level, turret #2 is raised by one deck, and turret #3 is raised by two decks. The only substantial difference from the prior Minneapolis class is that the #1 turret has its on-mount backup rangefinder deleted in order to save weight.
The secondary battery is arranged with a forward centerline 5" mount directly behind the #3 main battery turret, two wing mounts on each side of the 01 level superstructure (one just aft of the conning tower and one just aft of the rear mast and funnels) and an aft centerline mount at the end of the aft superstructure, slightly raised so that it can fire over the aft side mounts.
The tertiary battery is arranged with one 1.1" quad mount on each side of the hangar roof forward of the catapults and two quad mounts side-by-side on the fantail. By the end of World War II, this has been increased to six 40mm Bofors autocannon quad mounts (two on each side of the hangar roof and two on the fantail), four 40mm Bofors autocannon twin mounts (one on each side of the main deck forward of the superstructure, one on each side of the forward deckhouse 03 level, and one on each side of the aft deckhouse 02 level), and typically twenty to thirty 20mm Oerlikon autocannons on single pedestal mounts.
Propulsion
The St. Pauls utilize the same turbo-electric plant as the Minneapolises, with six boiilers and three turbine sets for six main generators and twelve electric motors.
Aircraft
The St. Pauls> are fitted with a longer and wider single-level aircraft hangar in place of the two-level hangar of the preceding class. The deck elevator is placed at the forward end of the hangar and the catapults at the aft end with the boat crane centered between them and folding flat when not in use. Four Curtiss SOC Seagull floatplanes are normally carried.
One catapult is later removed and the remaining catapult moved to the centerline of the roof.
(The St. Paul class is a counterpart to both the Baltimore class heavy cruiser and Cleveland class light cruiser.)
Salem Class Cruiser (1943)
The Salem class cruisers are the U.S. Navy's last and most powerful light cruisers, fitted with fully automatic rapid-fire seven-inch guns. Congress authorizes twelve cruisers of this class in 1943 and twelve in 1944, although only nine were ultimately completed as designed (three incomplete hulls were redesigned as missile cruisers).
Scout Cruisers
The U.S. Navy historically built very few scout cruisers due to the concentration on dreadnoughts in the 1905-1915 time frame and on mass production destroyers from 1916 onwards. A relatively substantial build of ten Omaha class scout cruisers were the first new warships built after World War I, but no further scout cruisers followed until the post-Treaty era.
Atlanta Class (1938)
The Atlanta class cruisers are a post-treaty class of small scout cruisers or large destroyer-leaders armed with 5" guns.
Design
The Atlanta class have a standard displacement of 6,000 long tons and measure 500 feet long at the waterline by a beam of 55 feet and a draft of 20 feet.
Armament
The Atlantas are armed with a main battery of twelve 5"38 Mark 12 guns in four triple turrets and a torpedo battery of sixteen 21" torpedo tubes in four quad mounts.
The main battery is arranged in a 2-A-2 configuration with a two turrets on the forward centerline and two turrets on the aft centerline. The #1 and #4 turrets are placed at deck level with the #2 and #3 turrets superfiring over them.
There was no secondary or tertiary battery fitted at the time of construction, but 20mm Oerlikon single mounts and 40mm Bofors twin mounts were later added.
The torpedo battery is arranged with two quad mounts on each side of the main deck, placed amidships.
Propulsion
The Atlantas have geared turbine propulsion, with four oil-fired boilers feeding 600 PSI, 750 F superheated steam to two turbine sets.
Aviation Cruisers
The U.S. Navy initially classifies aircraft carriers as "aviation cruisers" in the belief that they would be best utilized in the scouting and skirmishing roles traditionally performed by cruisers. However, the advent of large aircraft carriers based on battlecruiser hulls soon leads to a vastly more ambitious concept of naval aviation in which carriers serve as primary strike assets, deploying large numbers of high-performance torpedo and dive bombers.
Under the terms of the Washington Naval Treaty, no limitations are placed on small aircraft carriers of 10,000 tons or less. Since this is the same tonnage limit that the treaty sets for cruisers, the U.S. Navy continues to use the "aviation cruiser" designation for the small carriers built under this clause.
"A" Class Aviation Cruiser (1925)
The "A" class aviation cruisers are designed as small, relatively well-protected aircraft carriers oriented towards providing defensive and scouting air support for a surface task force. While built from the keel up as carriers, they are based on armored cruiser hulls and feature an armored flight deck and relatively heavy anti-aircraft armament.
The As are designed to accomodate a small air wing of one scout and two fighter squadrons.