クラ湾夜戦
After making two Tokyo Express runs from Rabaul to Kolombangara and Rekata Bay in January 1943, "Mochizuki" returned to Sasebo for repairs. She returned to Rabaul at the end of March, assisting the torpedoed "Florida Maru" along the way. Through the end of June 1943, "Mochizuki" was used as a Tokyo Express transport to Rekata, Buna, Tuluvu and Kolombangara. During the Battle of Kula Gulf on 5–6 July, "Mochizuki" engaged the destroyers and , taking minor damage from shell hits on her No. 1 gun turret and torpedo tubes. The damage was severe enough to warrant a return to Sasebo to the end of August. After returning to Rabaul at the end of September, "Mochizuki" resumed Tokyo Express operations