[4] However, his time with St Kilda was unsuccessful, playing only one game in the lone season he was at the club.

[3][7] He began his service as a Second Lieutenant in the 58th Battalion,[3][7] with which he would remain for the entirety of World War I, and embarked from Melbourne, Victoria on 16 December 1916, on the HMAT A7 Medic.

[3][7] The 58th Battalion was attached to the 5th Australian Division and saw action in Egypt[5] and on the Western Front, fighting in France[5] and Belgium.

Flintoft fought in many of the deadliest battles of World War I, such as Fromelles, Amiens and Mont St. Quentin.

Flintoft, however, remained unharmed throughout World War I, was promoted to the rank of Lieutenant, and returned to Australia on 3 March 1919.