This was the Japanese seizure of Nauru and Ocean islands in the western part of the central Pacific (29/30 August 1942).
The undertaking was to have been implemented immediately after ‘Mo’ (ii) and before ‘Mi’ (ii) in order to provide Japan with the islands’ abundant quantities of phosphate, one of the starting points for the creation of effective fertilisers and for the phosphorus used in the manufacture of explosives.
Nauru island lies some 155 miles (250 km) to the north-west of Ocean island and about 390 miles (630 km) to the west of the Gilbert islands group, and the two islands were under Australian mandate control with the British Phosphate Commission running the mining operations associated with the manufacture of ammunition, explosives and fertilisers.
The German armed merchant raiders Orion and Komet sank five merchant ships and undertook a gunfire bombardment of Nauru island on 6 December 1940, causing damage to the phosphate mining operation and disrupting the Allied production of phosphate. After the raids, the Australian naval authorities requested British Admiralty agreement for the redeployment of Australian naval units to meet an repeat attack by German raiders. The Australian armed merchant cruiser Manoora arrived off Ocean island on 4 January 1941, and Australian and New Zealand warships maintained a continual presence off the islands during the subsequent months. A naval company and two field guns were deployed on each island.
The attacks also led to the introduction of convoys between Australia and New Zealand. Late in February 1942, the fear of a Japanese invasion of Nauru and Ocean islands prompted the despatch of a merchant ships, escorted by the Free French destroyer Triomphant, from the New Hebrides islands group to evacuate both Nauru and Ocean islands. The ships arrived on 23 February, and all European civilians were evacuated in the merchantman.
Though ‘Mo’ (ii) was cancelled on 8 May 1942, immediately following the Battle of the Coral Sea, Japanese naval forces left Rabaul on New Britain island and Bougainville island in the Solomon islands group on 11 May for ‘Ry’.
Rear Admiral Kiyohide Shima’s invasion force comprised the light cruiser Tatsuta, minelayers Okinoshima (flagship) and Tsugaru, and destroyers Uzuki and Yuzuki. Cover was provided by Vice Admiral Takeo Takagi’s 5th Cruiser Division (heavy cruisers Myoko and Haguro) and Destroyer Division 30 (Ariake, Mochizuki, Shigure and Shiratsuyu). The 6th Special Naval Landing Force and Kashima Special Naval Landing Force were carried by the transports Kinryu Maru and Takahata Maru.
Off New Ireland, Okinoshima was torpedoed and severely damaged by the US submarine S-42 on 12 May. The invasion force’s convoy escorts depth-charged the area for more than six hours, until 11.30, causing damage to S-42 and persuading the captain to return to base at Moreton Bay near Brisbane in Australia. With Mochizuki towing Okinoshima, Shima transferred to the destroyer Yuzuki to the south-west of Buka island off Bougainville. At 06.40, Okinoshima capsized and sank in St George’s Channel of the Bismarck Sea. Despite Okinoshima’s loss, the rest of the Japanese force continued the operation.
As these forces were en route, however, a Japanese scout floatplane from Tulagi sighted the US fleet carriers Enterprise and Hornet heading toward Nauru island. On the basis of intelligence derived from intercepted Japanese communications, the carriers had been sent to the area as a feint to try to stop the Japanese operation. The feint was successful and, fearing the threat posed by the US carriers to the ‘Ry’ forces, which lacked any type of air cover, the Japanese cancelled the operation on 15 May and the forces returned to Rabaul.
Departing Truk island in the Caroline islands group on 26 August 1942, the second invasion force comprised the light cruiser Yubari, destroyers Oite, Yuzuki, Ariake, Yugure and Yunagi, and transport Hakozaki Maru. Men of the 43rd Guard Force and 62nd Guard Force landed on Nauru island and Ocean island respectively on 29 and 30 August without encountering any opposition.
The Japanese held Nauru island until 14 September 1945, when Captain Saeda’s garrison surrendered to an Australian officer, Brigadier John R. Stevenson, delivered by the Australian frigate Diamantine, and held Ocean island until 1 October, when Commander Suzuki’s garrison surrendered.