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.
For its treaty cruisers, the alternate U.S. Navy chooses not to simply use the largest-caliber guns permitted. Instead, it accepts a delay in laying down new cruisers to allow the Bureau of Ordnance to compare the effectiveness of various intermediate caliber naval guns taken from pre-dreadnoughts and armored cruisers which are now being scrapped. BuOrd concludes that 7" (178mm) is still the largest calibre practical for a rapid-fire naval gun and 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.
(Historically, the United States built a total of eighteen 8" armed treaty cruisers under the Washington Naval Treaty, followed by nine 6" armed light cruisers under the London Naval Treaty. In the alternate timeline, "only" ten treaty cruisers are built since resources have to be shared with the six larger armored cruisers.)
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)
The Minneapolis class cruisers are the U.S. Navy's final class of treaty cruisers. The signature characteristics of this class are the adoption of an all-forward semi-superfiring main battery and a dual-purpose secondary battery. Congress authorizes two in 1934 and a further four in 1935.
Design
The Minneapolises have a standard displacement of 10,000 tons and are shorter but wider than their predecessors, measuring 550 feet at the water line with a beam of 70 feet and a mean draft of 18 feet. The hull is still flush deck for strength, but is considerably refined for better seakeeping, with a high overall freeboard, a bulbous bow, transom stern, and twin semi-balanced rudders placed inline with the inboard shafts.
Armament
The Minneapolises are armed with a main battery of twelve 7"⁄45 Mark 4 guns in three four-gun turrets and a secondary battery of ten 5"⁄38 Mark 12 dual purpose guns in five twin turrets. Central fire-control directors and full remote power control (RPC) are fitted for both the primary and secondary batteries, and later augmented with radar. Space is set aside for sixteen 1.1"⁄75 anti-aircraft autocannons in "Chicago Piano" quad mounts, but due to unforeseen delays in development these guns are not actually available until several years after commissioning.
The main battery is arranged in a 3-A-0 configuration with all three turrets in a semi-superfiring trio on the forward centerline: #1 at the main deck level, #2 raised by one deck, and #3 raised by two decks. The 7"⁄45 Mark 4 guns introduce one-piece monobloc barrels with autofretted liners, dramatically decreasing gun weight from over eighteen tons per gun to barely ten tons. This enables the four-gun turrets to be no heavier than the previous triple turrets and to have an increased maximum elevation of fifty degrees. The guns can be loaded at a rate of six to eight rounds per minute while at 0 to 15 degrees elevation, and the shell handling equipment is sized for 215-pound "superheavy" AP shells in addition to standard 165-pound AP and HE shells.
The secondary battery is arranged with two wing mounts on each side of the 01 level superstructure and one centerline mount at the end of the aft superstructure (above the vestigial fantail). The mountings are twin-gun derivatives of the single mounts developed for the USN’s new destroyers, with a fully enclosed rotating gunhouse seated on a base ring over a handling room containing the upper ammunition hoists.
The tertiary battery is arranged with one 1.1" quad mount on the roof of the #3 main battery turret, one quad mount on each side of the hangar roof (forward of the catapults), and one quad mount on the fantail. By the end of World War II, this has been increased to five 40mm Bofors quad mountings (one on top of #3, one on each side of the hangar roof, and two on the fantail), four 40mm Bofors twin mountings (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 Minneapolises are the first cruisers fitted with a turboelectric propulsion plant, with six Babcock and Wilcox oil-fired boilers feeding superheated steam to three paired sets of turbines. The boilers and generators are arranged as a unit system with three centerline turbogenerator rooms each containing a high-pressure and low-pressure turbine pair, two 450-volt AC main turbogenerators, and two 120-volt DC auxiliary ship’s service turbogenerators. Six individual boiler rooms are placed to the port and starboard of the turbogenerator rooms, with two auxiliary machinery rooms placed between the three boiler rooms on each side. The primary control space is located between the #1 and #2 turbogenerator rooms, and an auxiliary control space is located between the #2 and #3 turbogenerator rooms. Further aft are four motor rooms, each containing three 9000-horsepower double-armature electric motors for a total propulsion plant output of 108,000 horsepower. This is a slight increase from previous cruisers, compensating for the wider beam.
Aircraft
The Minneapolises have substantially increased aircraft handling facilities over prior cruisers, with a two-level aircraft hangar forming the central section of the ship’s superstructure. This hangar provides sufficient space to store two floatplanes on the upper level while carrying out repairs and maintenance on the lower level. A small deck elevator is used to move floatplanes between the hangar levels and the two catapults on its roof, with a single large boat crane for catapult mounting and recovery. Four Curtiss SOC Seagull floatplanes are normally carried.
One catapult is later removed and the remaining catapult moved to the centerline of the roof.
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 (1936)
The St. Paul class cruisers are the U.S. Navy's first post-treaty cruisers, essentially enlarged repeats of the Minneapolis class. Congress authorizes four in 1936, eight in 1938, twelve in 1940, eighteen in 1941, and eighteen in 1942 for a total of sixty, the largest class of cruisers ever ordered.
Design
The St. Pauls have a standard displacement of 12,500 long tons and measure 575 feet at the waterline with a beam of 75 feet and a draft of 20 feet. They are distinguishable from their predecessors by the addition of a centerline secondary gun mount directly behind the #3 main battery turret.
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.)
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.