Helena was sunk in the Pacific, and while some of the others were heavily damaged, the remaining ships of the class were decommissioned shortly after the end of the war.

[2] The desire for the Brooklyns arose from the London Naval Treaty of 1930, which limited the construction of heavy cruisers, i.e., ships carrying guns with calibers between 6.1 and 8 inches (155 and 203 mm).

Agreement to the London Treaty and the proceeding with the American light cruiser design can be focused to Admiral William V. Pratt, who overrode the vehement objections of the General Board.

[4] The United States needed large cruisers to deal with the extreme ranges that operations in the Pacific Ocean required.

The last two ships of the class, St. Louis and Helena, were slightly modified versions of the design with new higher pressure boilers and a unit system of machinery that alternated boiler and engine rooms to prevent a ship from being immobilized by a single unlucky hit; this system would be used in all subsequent US cruisers.

They could be distinguished visually from the other Brooklyns by the placement of the after deckhouse, immediately abaft the second funnel, and by the twin 5-inch mounts.

[9] The impact of the shell changed the General Board's view on the usefulness of light cruisers in service.

The intention to mount 1.1-inch (28 mm)/75 caliber anti-aircraft guns was frustrated and the requirement was not fully met until 1943.

A late World War II refit saw the Mk 51 director installed for the Bofors guns.

[13] The vast majority of cruisers built by the United States during World War II derive from the Brooklyn design.

After being repaired in the United States, Honolulu returned to service only to be torpedoed by a Japanese aircraft on 20 October 1944, during the invasion of Leyte.

[17] On 11 September 1943, Savannah was hit by a German Fritz X radio guided bomb which penetrated her #3 turret and blew out the bottom of the ship.

While under repair in the United States, Savannah and Honolulu were rebuilt with a bulged hull that increased their beam by nearly 8 feet (2.4 m) and their 5-inch/25 caliber guns were replaced by four twin 5-inch/38 caliber guns, although the repairs to Savannah were completed too late for her to see frontline action again.

Six were sold to South American countries in the early 1950s, and served for many more years: Brooklyn and Nashville to Chile, St. Louis and Philadelphia to Brazil, and Boise and Phoenix to Argentina.

ARA General Belgrano (ex-Phoenix) was torpedoed and sunk by HMS Conqueror during the Falklands War,[19] while O'Higgins (ex-Brooklyn) remained in service with the Chilean Navy until 1992.