Born in Manly, New South Wales, Australia, the son of Charles Croker Longmore and Janet Murray, he was educated at Benges School, Hertford and Foster's Academy, Stubbington before entering Dartmouth Naval College. He was commissioned into the Royal Navy in 1904. Having developed an interest in flying, he obtained his flying certificate in 1911. That year, assisted by Oswald Short of Short Brothers, he devised a way of mounting streamlined air bags on the undercarriage struts and under the tail of an Short Improved S.27 biplane bearing Admiralty number 38—later often referred to as the "Short S.38"—and on 1 December 1911, using the air bags for flotation, then-Lieutenant Longmore became the first person in the United Kingdom to take off from land and make a successful water landing in a sea