On 29 February 1940, at the age of sixteen, he enlisted with the Second Australian Imperial Force, taking his older brother's name and date of birth to ensure entry.

He served in the Semut I operation in North Borneo, and was parachuted behind enemy lines to conduct guerrilla warfare with the assistance of local fighters in early June 1945.

[3] The original recommendation for the award states:[4] ...he quickly formed a small guerilla [sic] force to harass the Japs escaping through the area.

In August he took charge of blocking the track from SAPONG estate west to MAHAMAN in conjunction with 9th Aust Div which he carried out with marked success, killing a further 4 Japs and capturing valuable intelligence reports and maps.

[6] Papers by Griffiths-Marsh about the training of his native guerrilla force and service in North Borneo are held at the Australian War Memorial.