On 4 December 1942, she departed San Francisco with transports bound for New Caledonia.
She shepherded the convoy into its Nouméan anchorage on the 21st, then shifted to Espiritu Santo, New Hebrides, where she proceeded into the Solomons.
She commenced operations there in January 1943 with bombardments of Japanese air facilities at Munda and Kolombangara, and during the next five months, repeated those raids and patrolled "the Slot" in the Central Solomons in an effort to halt the "Tokyo Express": reinforcement and supply shipping that sought, almost nightly, to bolster Japanese garrisons.

Shortly after midnight on 4–5 July, she participated in the bombardment of Vila and Bairoko Harbor, New Georgia.
Her division, Cruiser Division 9 (CruDiv 9) and its screen, Destroyer Squadron 21 (DesRon 21), then retired back toward Tulagi to replenish as troops were landed at Rice Anchorage.
Early on the morning of the 6th, however, the force located and engaged ten enemy destroyers headed for Vila with reinforcements embarked.
In the Battle of Kula Gulf, Helena and two enemy ships were sunk.

Six nights later, the force, TF 18, reinforced by DesRon 12, moved back up "the Slot" from Tulagi, and soon after 0100 on the 13th, engaged an enemy force consisting of the Japanese cruiser Jintsu and five destroyers in the Battle of Kolombangara.
During the battle, which raged for over an hour, Jintsu and Gwin were sunk and HMNZS Leander, Honolulu, and St. Louis were damaged.
St. Louis took a torpedo which hit well forward and twisted her bow, but caused no serious casualties.

She returned to Tulagi on the afternoon of the 13th.
From there, she moved on to Espiritu Santo for temporary repairs, then steamed eastward, aft forward to protect the bow, to Mare Island, to complete the work.
In mid-November, she returned to the Solomons, and from the 20th–25th covered Marines fighting for Bougainville Island.
In December, she returned to that island to shell troop concentrations and, in January 1944, shifted southward to bombard enemy installations in the Shortland Islands.
Then, she moved back to Bougainville to cover the landing of reinforcements at Cape Torokina.
On 4 December 1942, she departed San Francisco with transports bound for New Caledonia. She shepherded the convoy into its Nouméan anchorage on the 21st, then shifted to Espiritu Santo, New Hebrides, where she proceeded into the Solomons. She commenced operations there in January 1943 with bombardments of Japanese air facilities at Munda and Kolombangara, and during the next five months, repeated those raids and patrolled "the Slot" in the Central Solomons in an effort to halt the "Tokyo Express": reinforcement and supply shipping that sought, almost nightly, to bolster Japanese garrisons.
Shortly after midnight on 4–5 July, she participated in the bombardment of Vila and Bairoko Harbor, New Georgia. Her division, Cruiser Division 9 (CruDiv 9) and its screen, Destroyer Squadron 21 (DesRon 21), then retired back toward Tulagi to replenish as troops were landed at Rice Anchorage. Early on the morning of the 6th, however, the force located and engaged ten enemy destroyers headed for Vila with reinforcements embarked. In the Battle of Kula Gulf, Helena and two enemy ships were sunk.
Six nights later, the force, TF 18, reinforced by DesRon 12, moved back up "the Slot" from Tulagi, and soon after 0100 on the 13th, engaged an enemy force consisting of the Japanese cruiser Jintsu and five destroyers in the Battle of Kolombangara. During the battle, which raged for over an hour, Jintsu and Gwin were sunk and HMNZS Leander, Honolulu, and St. Louis were damaged. St. Louis took a torpedo which hit well forward and twisted her bow, but caused no serious casualties.
She returned to Tulagi on the afternoon of the 13th. From there, she moved on to Espiritu Santo for temporary repairs, then steamed eastward, aft forward to protect the bow, to Mare Island, to complete the work. In mid-November, she returned to the Solomons, and from the 20th–25th covered Marines fighting for Bougainville Island. In December, she returned to that island to shell troop concentrations and, in January 1944, shifted southward to bombard enemy installations in the Shortland Islands. Then, she moved back to Bougainville to cover the landing of reinforcements at Cape Torokina.
USS St. Louis (CL-49)