Crosbie was born in Mount Vernon, Newlyn, Cornwall to Norman Garstin and Louisa ‘Dochie’ née Jones.
[5] On returning home his father, fed-up with Crosbie's inability to get suitable qualifications and hold down a job, sent him to South Africa.
[6] With the outbreak of the First World War, he came back to Britain and in October 1914 joined B Squadron of King Edward's Horse as a private.
[6] He was commissioned on the battlefield as a 2nd lieutenant on 14 September 1915, and joined C Squadron, which was attached to the 47th (London) Division at Nœux-les-Mines and was involved in the Battle of Loos and on the Italian Front.
[9] His younger brother Denis was also a published poet and contributor to Punch, as well as an accomplished soldier, journalist, diplomat, and international traveler; he was killed in action during World War I.