She was designated as an auxiliary submarine chaser at the Kure Naval District and her conversion was completed at the Innoshima, Hiroshima shipyard of Osaka Iron Works on 24 October 1941. Her commanding officer was Reserve Lieutenant (J.G.) Suzuki Kanji (鈴木完爾). She was attached to the 91st Subchaser Division (along with auxiliary subchaser "Shonan Maru No. 6" and auxiliary netlayer "Choko Maru"), 9th Base Force, Southern Expeditionary Fleet, Combined Fleet. The 9th Base Force was based at Cam Rahn Bay, French Indochina which had been seized from the French in September 1940. On 3 January 1942, the Combined Fleet in anticipation of having to defend its newly acquired territories, reorganized. The Southern Expeditionary Fleet was renamed the 1st Expeditionary Fleet and tasked with defending French Indochina, Singapore, Thailand, and Burma; and the 2nd Southern Expeditionary Fleet was formed out of the Third Fleet and tasked with defending the Dutch West Indies. On 10 April 1942, the 1st, 2nd, and 3rd Expeditionary Fleets (created in 3 January 1942 and responsible for the Philippines) were placed under the unified command of the Southwest Area Fleet headquartered in Manila. The 1st Expeditionary Fleet (headquartered in Singapore) consisted of the 9th Base Force (Penang), the 10th Base Force (Singapore); the 11th base Force (Saigon), and the 12th Base Force (Andaman Islands).