After building seven ships to the original design, additional changes were incorporated, particularly to the propulsion machinery and the secondary battery, resulting in what is sometimes referred to the St. Louis sub-class, which also included Helena.

The ship was initially based in Norfolk, Virginia, for sea trials; her shakedown cruise concluded on 6 October, by which time World War II had broken out in Europe.

The unit left San Francisco on 6 January 1942 as an escort for troop ships carrying a Marine expeditionary force to American Samoa to strengthen the garrison there.

In response, the Japanese sent several submarines and elements of the 1st Air Fleet to launch a counter-attack, but they recalled both groups before making contact with either American task force.

[9] At that time, the unit also included her sister ships Honolulu and Nashville, the heavy cruisers Louisville and Indianapolis, and fourteen destroyers, commanded by Rear Admiral (RADM) Robert Alfred Theobald.

She moved first to Espiritu Santo in the New Hebrides, and from there, embarked on her first offensive operations in January 1943, conducting bombardments of Japanese positions at Munda and Kolombangara, particularly targeting the airfields there.

[18] St. Louis and the rest of TF 68 conducted a sweep into Vella Gulf on the night of 6–7 May to distract Japanese attention from a group of fast minelayers that laid a minefield off New Georgia to block re-supply efforts.

[19] On 12 May, TF 68 made another raid on Japanese positions in the area; St. Louis and the destroyers Jenkins and Fletcher were detached from the main force to bombard Munda while the rest of the ships attacked Vila.

[20] The invasion of New Georgia began on 30 June; St. Louis and the rest of TF 68 patrolled at the northern end of the Coral Sea; at that time, she cruised with Helena, Honolulu, and their escorting destroyer screen that consisted of O'Bannon, Nicholas, Chevalier, and Strong.

Captain Kanaoka Kunizo, the senior destroyer commander in charge of the reinforcement operation, decided to withdraw as well to avoid engaging a superior force with his ships loaded with soldiers and supplies.

Niizuki, the only radar-equipped destroyer, directed the aim of all three vessels, which launched a total of fourteen Long Lance torpedoes before withdrawing at high speed to escape back to Bougainville.

O'Bannon and Chevalier were detached to pick up survivors while Ainsworth prepared to search for the submarine he assumed to have been responsible, as none of his ships had detected the three Japanese destroyers on their radars.

Shortly thereafter, Ainsworth received orders from Halsey to return to Kula Gulf, as reconnaissance aircraft had spotted Japanese destroyers departing from Bougainville to attempt the planned reinforcement run that he had inadvertently disrupted the night before.

Niizuki—now the flagship of Rear Admiral Teruo Akiyama—and the destroyers Suzukaze and Tanikaze were to escort the other seven destroyers—Nagatsuki, Mochizuki, Mikazuki, Hamakaze, Amagiri, Hatsuyuki, and Satsuki—carried 2,400 troops and supplies.

As the Americans steamed toward Kula Gulf, the crews got their vessels ready for action, including closing all of the watertight doors to reduce the risk of flooding and turning off all lights to prevent detection by the Japanese.

The Japanese destroyers had already entered the gulf and begun unloading their cargoes; Niizuki detected the American ships on her radar at 01:06 at a range of about 13 nmi (24 km; 15 mi).

[27] Ainsworth instructed his ships to turn to the right at 02:03 to begin engaging the second group of destroyers, but shortly thereafter three of Suzukaze's or Tanikaze's torpedoes struck Helena on the port side, inflicting serious, ultimately fatal damage.

Ainsworth and the other vessels' captains were not immediately aware that Helena had been disabled owing to the course change, the general confusion that resulted from heavy smoke and gunfire during the battle, and the fact that most attention was directed at the oncoming second group of Japanese destroyers.

Shortly after 01:00 on 13 July, the Allies encountered the Japanese force commanded by Rear Admiral Shunji Isaki, which was composed of the light cruiser Jintsu and five destroyers, escorting a group of four destroyer-transports.

In the ensuing Battle of Kolombangara, Jintsu and the destroyers launched a spread of torpedoes at the Allied squadron before the cruisers closed to within 10,000 yd (9,100 m), where their gunnery control and search radars could effectively direct their shooting.

She steamed first to Espiritu Santo for temporary work that would allow her to make the crossing to Mare Island Navy Yard, where permanent repairs were carried out.

The ship's ventilation system was damaged, the communication line to the aft engine room was severed, and both of her aircraft were disabled, but St. Louis remained on station, albeit at the reduced speed of 18 knots (33 km/h; 21 mph).

The next day, another Japanese air strike failed to inflict any further damage to St. Louis, but she was nevertheless detached to return to Purvis Bay for repairs that lasted until the end of the month.

[9] St. Louis left the Solomons on 4 June, bound for the Marshalls, where she joined Task Force 52, which had been formed for the invasion of the Mariana and Palau Islands campaign in the central Pacific.

She reached Guam two days later and on the afternoon of 17 July, provided fire support as underwater demolition teams (UDT) dismantled fixed defenses at the planned landing sites.

At around 11:30, a second wave of ten aircraft arrived, and at 11:38, a D3A dive bomber on a kamikaze attack struck the ship, detonating its remaining fuel and the bomb it was carrying.

In October, the ships sailed to Shanghai, China, and later that month, she took part in an operation to move elements of the Chinese Army to Taiwan, which had been under Japanese occupation.

[9] During a period of political instability in 1955, Carlos Luz briefly seized power after the acting president, Café Filho, fell ill on 8 November.

Luz was himself deposed three days later, and he fled aboard Tamandaré, which was moored in Guanabara Bay off Rio de Janeiro, awaiting work on her boilers.

Luz sought to flee the capital to Santos, and when the ship passed out of the bay, the coastal fortifications guarding its entrance opened fire on Tamandaré, but scored no hits.