Japanese seaplane tender Sanuki Maru

She participated in the invasion of Batan Island, the opening campaign of the invasion of the Philippines, which began simultaneously with the Japanese attack on Pearl Harbor. The occupation force was tasked with establishing an air base to support future operations against American forces on Luzon as Batan Island is equidistance between Taiwan and Luzon.[5] The task force consisted of the destroyer Yamagumo as flagship with Sanuki Maru with its floatplanes to provide reconnaissance and air support along with the 52nd Subchaser division (Shonan Maru No. 17, Takunan Maru No. 5, Fukuei Maru No. 15), the 53rd Subchaser Division (Korei Maru, Kyo Maru No. 2, Kyo Maru No.11), the 54th Subchaser Division (Nagara Maru, Shonan Maru No. 1, Shonan Maru No. 2), Imperial Japanese Army transport Teiun Maru (carrying part of the 24th Airfield Battalion),[6] Imperial Japanese Navy transport Kumagawa Maru (carrying a 490-man unit of the Sasebo Special Naval Landing Force), four Chidori-class torpedo boats (Chidori, Manazuru, Tomozuru, Hatsukari), two W-13-class minesweepers (W-13, W-14), two patrol boats (Patrol Boat No. 1, Patrol Boat No. 2), two Tsubame-class minelayers (Kamome, Tsubame), three converted gunboats (Aso Maru, Koso Maru, Nampo Maru),[7] and destroyer Tachikaze.[4][8]

On 8 December 1941, four planes from the Sanuki Maru bombed the airstrip at Basco[8] and the 490 troops of the SNLF landed and quickly secured the existing small airfield outside Basco without resistance. On 9 December, the air corps troops began expansion work to make it suitable for fighters and reconnaissance aircraft with the first planes of the Imperial Japanese Army Air Service 24th and 50th Fighter Regiments landing at Basco that same day.[9] The Sanuki Maru then proceeded to Camiguin Island along with the ships of the 3rd Gunboat Division and Patrol Boat No. 1 (which carried a platoon of SNLF).[8] They met no resistance and established a floatplane base to support the pending invasion of Aparri. The destroyer Tachikaze (with a platoon of the Yokosuka SNLF) proceeded to occupy Calayan Island also meeting no resistance.[8] Patrol Boat No. 2 was dispatched to survey Fuga Island but found the terrain too steep to land a ground force.[8] The Sanuki Maru remained off Camiguin Island with gunboat Aso Maru to provide air support for the Japanese landings at Vigan, Aparri, and Gonzaga.[4] Six of her planes were damaged beyond repair due to rough sea conditions and the seaplane base at Camiguin Island was abandoned.[4] On 18 December 1941, she was replenished with 6 Mitsubishi F1M "Pete" floatplanes with her two remaining E8N2 "Dave" floatplanes held in reserve.[4]

She then departed for newly occupied Vigan, Luzon arriving on 21 December 1941 where she helped to establish a seaplane base with fellow seaplane tender Sanyo Maru contributing her 6 F1Ms along with 6 F1Ms and an Aichi E13A "Jake" from the Sanyo Maru and 3 Kawanishi E7K "Alf"s from light cruisers Naka and Natori.[4] The planes went on to support the landings at Lingayen.[4] That same day, she left Vigan heading southward to support the occupations of Jolo and Davao.[4] On 23 December 1941, as she approached Davao, she was hit by American shore batteries but only slightly damaged.[4] After arriving at Davao on the same day, the harbor was attacked by six Netherlands Naval Aviation Service Dornier Do 24 flying boats (squadrons GVT-2 and GVT-5) which damaged the station tanker Tonan Maru No. 2.[10] A F1M from the Sanuki Maru was credited with downing one of the flying boats.[10] She then joined the carrier Ryūjō and fellow seaplane tender Chitose to provided air cover for the Jolo invasion convoy which consisted of four Imperial Japanese Army transports (Havana Maru, Kuretake Maru, Teiryu Maru, Tsuruga Maru) and four Imperial Japanese Navy transports (Koshin Maru, Nichian Maru, Eiko Maru No. 2, unknown maru) carrying 4,000 men of the 56th Mixed Infantry Corps and the Kure No. 1 Special Naval Landing Force. The convoy is escorted by light cruiser Jintsū and four destroyers (Hayashio, Kuroshio, Natsushio, Oyashio).[11] After the successful occupation of Jolo, she returned to Davao and on 6 January 1942, she docked off the west coast of Samal Island.[1]

On 7 January 1942, Sanuki Maru and her fellow seaplane tender Sanyo Maru, provided air cover for the Tarakan invasion convoy which carried the 56th Mixed Infantry Group of Major General Sakaguchi Shizuo (jp:坂口静夫) (known as the Sakaguchi brigade) and the Kure No. 2 Special Naval Landing Force on nine Imperial Japanese Army transports (Tsuruga Maru, Liverpool Maru, Havana Maru, Kuretake Maru, Nichiai Maru, Hiteru Maru, Teiryu Maru, Jankow Maru, Ehime Maru), and five Imperial Japanese Navy transports (Kunikawa Maru, Kano Maru, Kagu Maru, Kokuto Maru, Rakuto Maru).[4] The two seaplane tenders joined the main convoy on 9 January 1942 and oversaw the successful occupation of Tarakan on 11 January 1942 (although the Dutch had destroyed the oil fields).[4] On 24 January 1942, the two seaplane tenders provided air cover for the highly successful invasion of Balikpapan, a major oil producing town and port, which carried the same units to Balikpapan, Borneo on 16 transports.[4] Although the Dutch commander ordered the destruction of oil installations in Balikpapan, it was not completed with the only serious damage done was to tanks, pipes and special quays in the harbor area.[12]

On 6 January 1945, she departed Moji in convoy Hi-91 headed for Singapore via Sasebo and Takao with transport Kitsurin Maru and tankers Tojo Maru and Eiyo Maru.[4] Her cargo was composed of 52 Type 1 explosive motorboats manned by 167 men of the 43rd Shinyo Squadron and 26 Type 5 explosive motorboat manned by 183 men of the 101st Shinyo Squadron.[4] The convoy was escorted by two destroyers (Nokaze, Kamikaze), two Ukuru-class escort ships (Shonan, Kume), and two Type C escort ships (CD-25, CD-53).[4] On 28 January 1945, while en route to Takao, U.S. submarines Spadefish and Pompon located the convoy in the Yellow Sea northeast of Shanghai.[4] Although two nighttime attacks by Pompon were unsuccessful, it occupied the convoy's escorts enabling Spadefish to draw close and fire three torpedoes at the Sanuki Maru all of which hit sinking her at 33°55′N 122°55′E.[4] The 183 men of the 43rd Shinyo Squadron and 133 men of the 101st Shinyo Squadron were killed.[4] Spadefish also sank Kume killing 89.[4] On 10 March 1945, she was struck from the Navy List.[1]