[2] At the age of twenty-one in 1930, Carnell appeared 9 times for North Sydney as a fullback.

[2][3] He enlisted as a private in the Second Australian Imperial Force on 28 March 1940, and was posted to the 2/12th Infantry Battalion on 27 April.

[3] Whilst serving with the battalion in November 1940, Carnell was subject to a general court martial for being found outside his barracks without a leave pass, "disobeying a lawful command given by his superior officer", and "offering violence to his superior officer", for which he was found guilty on all counts and given detention for thirty days.

[3] He and his battalion participated in the North African campaign, and Carnell served during the Siege of Tobruk in 1941, during which he was promoted to lance corporal.

[3] The battalion was then given a rest period, during which Carnell was admitted to hospital and had his rank demoted to private upon his own request.