This abbreviation, now part of the popular vernacular, was used by Admiral of the Fleet John A. (Jackie) Fisher (1841 – 1920), 1st Baron Fisher, in a letter written to The Hon. Winston Churchill MP. These two were close friends and frequent correspondents; Lord Fisher was the First Sea Lord from 1904 to 1910 and also from 1914 to 1915, while Churchill was the First Lord of the Admiralty from 1911 to 1915. You can read about this here. more