After building seven ships to the original design, additional changes were incorporated, particularly to the propulsion machinery and the secondary battery, resulting in the St. Louis sub-class, of which Helena was the second member.

After entering service, the ship was occupied with sea trials and initial training, and she embarked on a major shakedown cruise abroad on 27 December, bound for South American waters.

While in the latter port, the crew inspected the wreck of the German heavy cruiser Admiral Graf Spee that had recently been scuttled after the Battle of the River Plate the previous month.

The ship's crew raced to their battle stations and two minutes after the torpedo hit, the backup forward diesel generator had been turned on, restoring power to the guns.

[21] As Helena's anti-aircraft guns got into action, they helped to fend off further attacks from the second strike wave while other men worked to control flooding by closing the many watertight hatches in the ship.

[17][26][27] Over the course of the next two months, Helena and the rest of TF 64 were occupied with covering reinforcement convoys to support the Marines fighting on Guadalcanal and escorting carrier battle groups in the area.

[17][28] By this time, the task force consisted of Helena, her sister ship Boise, the heavy cruisers San Francisco and Salt Lake City, and the destroyers Farenholt, Duncan, Buchanan, McCalla, and Laffey.

[29] Following the Actions along the Matanikau in late September and early October, the decision was made to send further reinforcements to the island, and so the 164th Infantry Regiment of the Americal Division embarked on a pair of destroyer transports; TF 64 provided the close escort for the vessels, screening them to the west to prevent Japanese forces from intercepting them.

By this time, the unit was commanded by Rear Admiral (RADM) Norman Scott, who conducted one night of battle practice with his ships on 8 October before embarking on the operation.

As the two squadrons approached each other in the darkness at the southern end of the Slot shortly before 22:00 on 11 October, three of the four American cruisers launched their floatplanes, but Helena did not receive the instruction from Scott aboard his flagship San Francisco, and so her crew dumped the aircraft overboard to reduce the risk of fire in the event of a battle.

This maneuver rewarded Furutaka with numerous shell hits from several warships including Helena, at least one of which detonated the torpedoes in her deck launchers and caused a major fire.

In the confused, close-range action, either Helena or Boise (the only ships armed with 6-inch guns) accidentally hit Farenholt, causing flooding and a fuel leak that forced her to withdraw from the battle.

Despite having been hit more than forty times, Aoba survived the battle, though Furutaka eventually succumbed to progressive flooding, as did Fubuki; Helena contributed to both vessels' demise.

Meanwhile, the Japanese had assembled a convoy of their own carrying 7,000 men and supplies for the army already on Guadalcanal; it was to be supported by a bombardment force of two fast battleships, a light cruiser, and eleven destroyers.

Abe's ships reached the area off Cape Esperance at around 01:25 on 13 November, by which time his vessels had fallen into disarray due to bad weather that greatly hampered visibility.

[56] Hoover, the senior surviving officer in the shattered American squadron, ordered all vessels still in action to withdraw to the southeast at 02:26 while the Japanese retreated in the opposite direction.

Admiral William Halsey subsequently relieved Hoover of command, citing his failure to ensure a prompt report of the sinking was made, to attack the submarine, or to mount rescue operations.

A "Black Cat" PBY Catalina provided spotting support while the two cruisers fired around 3,500 shells from the main and secondary gun, inflicting significant damage on the airfield and equipment.

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

The other vessels quickly joined in the bombardment, which lasted about fourteen minutes before the American column turned east to move to the Rice Anchorage to shell targets there.

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.

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.

[78] 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 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.

In light of Ainsworth's order to avoid being caught by Japanese aircraft and with daylight fast approaching, Nicholas and Radford withdrew, leaving four of their whaleboats behind to help ferry men to American positions on New Georgia.

A B-24 Liberator heavy bomber passed the area at low altitude to search for survivors and its pilot reported seeing the men who had climbed aboard the floating bow along with other groups in the water.

The flotilla arrived back in Tulagi that afternoon and disembarked the survivors, who were then transferred to the French colony of New Caledonia, where they met the men who had been pulled from the water on the night of the sinking.