The island experienced an influenza epidemic in 1920, with a mortality rate of 18 per cent among native Nauruans.[17] In 1923, the League of Nations gave Australia a trustee mandate over Nauru, with the United Kingdom and New Zealand as co-trustees.[18] 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 shiploading cantilever.