Japanese ground forces were already retreating in New Guinea and in the Solomon Islands, abandoning Guadalcanal, Kolombangara, New Georgia and Vella Lavella.

Simpson Harbour—captured from Australian forces in February 1942—was known as "the Pearl Harbor of the South Pacific" and was well defended by 367 anti-aircraft guns and five airfields.

[4] Admiral William Halsey was implementing the next phase of his advance up the Solomon chain and looked to establish a base on Bougainville.

On Bougainville the Japanese had two airfields at the southern tip of the island, one at the northernmost peninsula, and a fourth on Buka just across the northern passage.

Instead of attempting a costly assault on these heavily defended areas, Halsey landed his invasion force of 14,000 Marines at Empress Augusta Bay, about halfway up the west coast of Bougainville.

[5] On the night of 1/2 November the screening naval unit succeeded in defending the landing (the Battle of Empress Augusta Bay), but Admiral Mineichi Koga responded quickly.

His main surface strength, two battleships and a number of cruisers, had been transferred to the Central Pacific to support the upcoming invasion of Tarawa.

These would have been considered a potent force for a battle at sea, but Rabaul was a heavily fortified port with five airfields and extensive anti-aircraft batteries.

With the exception of the surprise raid at Pearl Harbor, no attack against such a formidable land target had been attempted by carrier aircraft.

Halsey later said the threat that the Japanese cruiser force at Rabaul posed to his landings at Bougainville was "the most desperate emergency that confronted me in my entire term as ComSoPac (Commander of the South Pacific Area).

"[6] With the fate of the landing in the balance, Halsey ordered his carriers, under command of Rear Admiral Frederick C. Sherman, to steam north through the night of 4/5 November to get within range of Rabaul for a daybreak raid on the base.

Aircraft from airfields on Barakoma and the recently captured Vella Lavella were sent out to sea to rendezvous with the carrier force to provide it with some measure of protection.

Atago suffered near misses by three 500 lb (230 kg) bombs that caused severe damage and killed 22 crewmen, including her captain.

[14] The destroyer Suzunami reportedly suffered a direct bomb hit while loading torpedoes near the mouth of Rabaul Harbor.

[15] In the wake of the raids the Japanese launched a series of counterattacks involving 120 aircraft against the U.S. carriers, but the force was intercepted and lost 35 planes without inflicting damage on Montgomery's ships.