Japanese submarine chaser CH-7 (1938)

In November 1941, she was assigned to the Borneo Invasion Group (under Rear Admiral Kurita Takeo), code-named "Operation B" (the invasion of British Borneo).[3] The force consisted of five Imperial Japanese Army transports carrying the 25th Army (Katori Maru, Hiyoshi Maru, Myoho Maru, Kenkon Maru, and Nichiran Maru); and five Imperial Japanese Navy transports (Hokkai Maru carrying the No.2 Yokosuka Special Naval Landing Force, Tonan Maru No 3 carrying the 4th Naval Construction Unit, and three transports carrying equipment and supplies, Unyo Maru No. 2, Kamikawa Maru, and Mitakesan Maru).[3] The force was escorted by CH-7 along with and two minesweepers (W-3 and W-6) while two heavy cruisers (Kumano, Suzuya), two light cruisers (Yura and Kinu), six destroyers (Fubuki, Murakumo, Shinonome, Shirakumo, Usugumo, Sagiri), provided distant cover; and a seaplane tender (Kamikawa Maru) provided air support.[3] On 13 December 1941, the convoy left Cam Ranh Bay, Indochina (Mitakesan Maru is later detached to deliver supplies to the Philippines). On 15 December 1941, the transports arrived and disembarked their troops unopposed at Seria, Miri, and Lutong, successfully occupying the airfields and oil wells. On 17 December 1941, the destroyer Shinonome was sunk by a Dutch Dornier Do 24 flying-boat flying from Tarakan.[3] CH-7 remained at Miri[1] with one battalion of the 25th Army while the rest of the force departed on 22 December 1941 to occupy Kuching.[3] On 25 December 1941, CH-7 left Miri arriving at Kuching on 26 December 1941.[2]

On 9 February 1942, she departed Camranh Bay as part of "Operation L" tasked with the invasion and occupation of Palembang and Banka Island, Sumatra.[2] The invasion force consisted of eight transports escorted by subchasers, CH-7 and CH-8; light cruiser Sendai; destroyers Fubuki, Hatsuyuki, Shirayuki, and Asagiri; and minesweepers W-1, W-2, W-3, W-4 and W-5.[2]

On 10 March 1942, she departed Singapore as part of "Operation T" tasked with the invasion and occupation of Northern Sumatra.[2] The invasion force consisted of 4 convoys carrying 22,000 soldiers including the Imperial Guards Division.[4] CH-7 served as escort along with section 1 of Minesweeper Division 44 for one of the convoys consisting of the minelayer Hatsutaka, submarine tender Nagoya Maru, and eight transports.[2] The force reached Sumatra unmolested on 12 March 1942 as Allied air and naval power had been severely reduced after the Battle of the Java Sea and the Dutch East Indies campaign.[4]

On 19 March 1942, she departed Camranh Bay as part of "Operation U" tasked with the reinforcement of Japanese troops in Burma.[2] The convoy is escorted by subchasers CH-7 and CH-8 along with a light cruiser Kashii (which serves as flagship), five destroyers (Shikinami, Asakaze, Harukaze, Hatakaze, and Matsukaze); an escort ship (Shimushu); a minelayer (Hatsutaka), 3 minesweepers (W-1, W-3, W-4); three submarine chasers (Choko Maru, Shonan Maru No. 5, Shonan Maru No. 7); a gunboat (Eiko Maru); an Ōtori-class torpedo boat (Kari), and an auxiliary gunboat (Kosho Maru).[2] The warships escorted the First Burma Transport Convoy consisting of 32 transports carrying the main body of the Imperial Japanese Army's 56th Division.[2]

On 14 July 1942, CH-7 is assigned along with CH-8 and CH-9 to Submarine Chaser Division 11, 10th Special Base Force, 1st Southern Expeditionary Fleet, Southwest Area Fleet.[2] She conducts various escort duties throughout southeast Asia primarily in the waters surrounding Vietnam, Indonesia, Singapore, and Malaysia.[2]

On 7 November 1944, she departed Manila for Singapore with CH-8 as escort for convoy MASHI-03 consisting of tankers Nichinan Maru No. 2 and Shimotsu Maru. On 8 November 1944, Nichinan Maru No. 2 was torpedoed and sunk by the USS Redfin (killing 86).[2] On 9 November 1944, Shimotsu Maru was torpedoed and sunk by the USS Barbero (killing 39).[2] The convoy was dissolved.[2]