Beach, Frederick C. & Rines, George E., eds. (1912); The Americana: A Universal Reference Library, Volume 9; Scientific American, NY. See Section 22, "Germany – The Colonies": "The German colonies belong to the World [sic] Postal Union. There is the same rate of postage for letters, papers, etc., sent to Germany and to each colony as within the German Empire."
Meyer, G.J. (2006); A World Undone: The Story of the Great War 1914 to 1918; Delacorte, USA; ISBN0-553-38240-3. See p.286: "The German Navy was born in 1898... Wilhelm II and Tirpitz had embarked upon the building of a navy that they hoped to make as powerful as Britain's...."
Chambers, William & Chambers, Robert (1917); Chambers's Journal, Vol. VII, Dec. 1916–Nov. 1917; See p. 262: "In retaliation for the British boycott [spoilage of German stamps], the German Governor of Belgium has imposed a heavy fine, accompanied by other pains and penalties, upon Belgian stamp dealers and collectors having in their possession any war-stamps of the Allies."
Littell, Eliakim & Littell, Robert S. (1917); The Living Age, Vol. 293; Boston USA. See p.291: "The German colonial postage-stamps, bearing a representation of the Imperial yacht Hohenzollern... were temporarily withdrawn from circulation... [and] reissued a few days later overprinted with the Royal cipher 'G.R.I.' and a new value in British currency."
