Built at Sasebo Naval Arsenal, Agano was completed on October 31, 1942 and originally assigned to Destroyer Squadron 10 of the Japanese Third Fleet. On December 16, 1942, Agano began her first combat operation, joining the Japanese aircraft carrier Junyō and other ships to escort troops to Wewak and Madang in New Guinea.Agano was next involved in the evacuation of Japanese troops from Guadalcanal, after which the ship received further minor modifications and repairs, before being assembled with powerful fleet units intended to counterstrike against American forces which had landed on Attu Island in the Aleutians. However, by the time the force was assembled, the Americans had completed their capture of the island, and the strike was called off.In June, 1943, Agano put in at Kure Naval Arsenal for refit, including the addition of air search radar Type 21 and ten 25 mm Type 96 antiaircraft guns in two twin and two triple mounts, adding to the original two triple mounts for a total of sixteen guns. After refitting and dry dock, Agano departed for Truk in the Caroline Islands with a large Japanese force. Despite numerous spottings by American submarines and an attack on the Japanese aircraft carrier Zuiho, Agano made it safely to Truk where she began ferrying troops to Rabaul.