The Minneapolis-class cruisers are the last U.S. Navy cruisers built under the restrictions of the Washington Naval Treaty. The U.S. Navy classifies its treaty cruisers as "light armored cruisers" and assigns them the new hull designation of "CL".
As late treaty era cruisers, the Minneapolises are generally compared to the British County-class, the Japanese Takao-class, the French Algérie-class, and the Italian Zara-class. The United States is the only signatory power which does not arm its treaty cruisers with the largest caliber guns (8") permitted under the treaty; instead, they are uniquely armed with lighter but more numerous and much faster-firing seven-inch guns.
Congress authorizes two cruisers of this class in 1934, four more in 1935, and a final four in 1936 for a total of ten.
Design
As treaty cruisers, the Minneapolises have a standard displacement of exactly 10,000 tons, although their actual full-load displacement is nearly 13,000 tons. They measure 600 feet long with a beam of 65 feet and a draft of 25 feet.
The superstructure is a semi-unified layout consisting of an octagonal 01 level which extends from the #2 turret forward to the #3 turret aft. Just clear of the #2 turret is a forward deckhouse wrapped around a lightly armored conning tower and extending to 04 level, and similarly just clear of the aft turret is a aft deckhouse to the 03 level. The ship's foremast extends from the aft portion of the forward deckhouse with the forward smokestack directly following, and the mainmast similarly extends from the aft deckhouse directly aft of the aft smokestack.
Details
Armament
The Minneapolises are armed with a main battery of twelve 7"⁄45 Mark 3 guns, a secondary battery of eight 5"⁄38 Mark 12 dual-purpose guns, and initially a tertiary battery of sixteen 1.1"75 Mark 1 autocannons. Like all warships serving into World War II, they are repeatedly refitted with increased tertiary AAA: 20mm Oerlikon autocannons in single and twin pedestal mounts starting in late 1940 and 40mm Bofors autocannons in twin and quad mountings starting in 1942.
Fire Control
The Minneapolises follow the Portland-class armored cruisers in adopting remote power control (RPC) for both the main battery and secondary battery turrets. This enables the ship to use its centralized fire control director equipment to directly transmit traverse and elevation commands to the turret drives rather than merely setting pointers for the on-mount crew to manually follow. Manual operation of the turrets via either pointer or purely local control remains available as a backup method of operation.
Main Battery
The main battery is arranged in a conventional 2-A-2 configuration with a superfiring pair of three-gun turrets on the forward centerline and a superfiring pair of three-gun turrets on the aft centerline.
All three treaty-era USN light cruiser classes carry the same basic main battery configuration, with the only major difference being that the Houstons and Minneapolises are designed with shorter barbettes for the superfiring turrets than the preceding Pensacolas. Instead of having a substantial vertical gap between the turrets, they are overlapped as closely as possible with the gun barrels of #2 and #3 having minimal clearance over #1 and #4.
Secondary Battery
The secondary battery is arranged in two twin wing mounts on each side of the main deck. The forward wing mounts are placed slightly aft of the conning tower so that they are clear of the forward main turrets firing at maximum traverse, and the aft wing mounts are similarly placed slightly forward of the mainmast to clear the aft main turrets at maximum traverse.
Tertiary Battery
The original tertiary battery is arranged with the 1.1" autocannons in four "Chicago Piano" quad mounts: one on each side of the forward superstructure 02 level (below the bridge wings) and one on each side of aft superstructure 01 level (flanking the mainmast).
The final tertiary battery consists of four 40mm Bofors quad mountings (replacing the original 1.1" mountings), eight 40mm Bofors twin mountings (two at the bow, one on each side fore and aft of the superstructure and two at the stern), and eight 20mm Oerlikon twin pedestals (four on an AA platform between the funnels, and four atop the forward part of the hangar roof).
Propulsion
The Minneapolises utilize a more compact geared turbine propulsion plant than previous light cruisers, with 600 PSI steam boilers.
Aircraft
The Minneapolises are the first U.S. Navy light cruisers to be fitted with enclosed storage space for their scout aircraft, which enables them to carry four floatplanes rather than two. They are initially assigned Curtiss SOC Seagulls, but from 1941 onwards these are replaced by Vought OS2U Kingfishers.
The aircraft hangar is incorporated into the aft deckhouse, with two large hangar doors opening forward to the amidships deck where the ships' catapults and recovery cranes are installed. Two scout planes can be stored in the aft portion of the hangar with their wings folded, while the forward portion provides workshop space to rig planes for launch and maintain them. In severe weather all four floatplanes can be secured in the hangar.