Garth was a Solicitor on enlistment in 1917. He served as Second Lieutenant 17417, 21st Reinforcements, Mounted Rifles Brigade, Machine Gun Section, NZEF. His next of kin was his father, R. K. Jackson, Solicitor of Masterton. He embarked on the Manuka 8 Feb 1917, then transfered to Morea at Sydney and Mashobra at Bombay for Suez