Corporal George Trevelyan initially embarked with the Samoan Advance Force as a Corporal in the 5th (Wellington) Regiment Machine Gun Section and was attached to the 3rd (Auckland) Regiment. They on 15th August 1914 from Wellington, NZ aboard either HMNZT 01 (ss Moeraki) or HMNZT 02 (ss Monowai) and disembarked 28th August 1914 at Apia, Western Samoa.

Given his rank and early embarkation date, he was most likely a member of the local Volunteer army unit prior to the war.

He subsequently embarked for France with the 25th Reinforcements NZEF in 1917 with the rank of Sergeant.  The 25th's embarked  26th April 1917 aboard both the HMNZT 83 (ss Tahiti) which disembarked 19th July 1917 at Plymouth, ENGLAND and HMNZT 84 (ss Turakina) which disembarked 20th July 1917 at Plymouth, ENGLAND.