John Fisher, known as “Jacky,” was an admiral and naval innovator who served as head of the British Navy during World War I, but resigned his post in 1915 after a falling out with Churchill over the disastrous Gallipoli campaign. While his naval career was over by the time he wrote his “dear Winston” the letter in 1917, one can only imagine he had become acclimated to speaking in coded messages and thus his ingenious use of OMG, which he helpfully explained to Churchill was an abbreviation for Oh! My God! Now if he could just explain what “Shower it on the Admiralty” means.
Promotion to midshipman came on 12 July 1856 and Fisher joined a 21-gun steam corvette , HMS Highflyer , part of the China Station .  He was to spend the next five years in Chinese waters, seeing action in the Second Opium War , 1856–1860. The Highflyer's captain, Charles Shadwell , was an expert on naval astronomy (subsequently being appointed a Fellow of the Royal Society in 1861) and he taught Fisher much about navigation, with spectacular later results.  When Shadwell was replaced as captain following an injury in action, he gave Fisher a pair of studs engraved with his family motto 'Loyal au Mort', which Fisher was to use for the rest of his life.