Nauru experienced an influenza epidemic in 1920, with a mortality rate of 18 per cent among native Nauruans. In 1923, the League of Nations gave Australia a trustee mandate over Nauru, with the United Kingdom and New Zealand as co-trustees. On 6 and 7 December 1940, the German auxiliary cruisers Komet and Orion sank five supply ships in the vicinity of Nauru. Komet then shelled Nauru's phosphate mining areas, oil storage depots, and the ship loading cantilever.
Japanese troops occupied Nauru on 25 August 1942. The Japanese built an airfield which was bombed for the first time on 25 March 1943, preventing food supplies from being flown to Nauru. Nauru, which had been bypassed and left to "wither on the vine" by American forces, was finally liberated on 13 September 1945, when commander Hisayaki Soeda surrendered the island to the Australian Army and the Royal Australian Navy