ブーゲンビル島沖海戦
After a voyage to Sydney, Australia, she joined Task Force 39 (TF 39) as its flagship for the invasion of the Treasury and Bougainville Islands. On 1 November, "Montpelier" shelled the Buka‑Bonis airfields on the northern tip of Bougainville, and hit the Japanese defenses on the islands of Poporang and Balalae, in the Shortlands. TF 39, consisting of cruisers and destroyers, engaged a superior Japanese force in the Battle of Empress Augusta Bay while guarding transports on the night of 2 November. The result was a victory for the U.S. ships commanded by Admiral Merrill. The victory turned back the Japanese from what would have been a disastrous assault on the Bougainville landing forces. Besides assisting in the destruction of one ship, "Montpelier"s gunners shot down five enemy planes.