Postage stamps and postal history of the Caroline Islands
Germany rapidly set up a postal system once awarded the islands; having received the Carolines on 1 June 1899 as part of the German-Spanish Treaty (1899), on 12 October German stamps overprinted "Karolinen" were issued. At first the overprint was angled at 48 degrees, then a few months later the angle of the text was changed to 56 degrees. Few examples of these, at either angle, survive today, especially in cancelled condition.
By 1900, Yap and Ponape were stops on a regular mail run between German New Guinea and Hong Kong. Initially the service was operated by the Reich Mail Steamer Lines, with the help of government subsidies, then in 1902 the Jaluit Company took over.
In January 1901, Germany issued its Yacht stamps with a common design for all of Germany's colonies, featuring the Kaiser's yacht Hohenzollern. The issues for the Carolines featured the inscription "KAROLINEN", all with mark and pfennig denominations. Many unused copies of the low values still exist today, left over after the Japanese occupation, but as one might expect from the short period of German rule and the very small numbers of letter-writers living in the Carolines, genuinely used stamps are uncommon, typically priced 5-20 times higher than unused.
Japan occupied the islands in October 1914, after which Japanese stamps were used until the end of World War II. Germany printed Yacht stamps for the Carolines as late as 1919, on paper with lozenge watermarks, but none were ever used on mail.