The ship escorted a convoy from Kwajalein to the naval base at Truk in January 1942, where a sponson was installed for a pair of license-built Type 93 anti-aircraft machineguns on the forward side of the bridge, and then to Guam. From February through March, she participated in the invasion of the Solomon Islands, covering the landings of Japanese forces during Operation R (the invasion of Rabaul, New Ireland and New Britain), and during Operation SR (the invasion of Lae and Salamaua on New Guinea), and in April, covering landings on the Admiralty Islands. During the Battle of the Coral Sea from 7–8 May 1942, "Mochizuki" was assigned to the Operation Mo invasion force for Port Moresby. After that operation was cancelled, it returned to Truk, escorting airfield construction convoys between Truk, Lae and Guadalcanal until recalled to Japan in mid-July for refitting.