'Messines Offensive, 7th to 9th June 1917. During the attack on Messines the Officer in command of No 8 Platoon was severely wounded and Sergt McMahon took command of the platoon and ably led it to the line on which the Platoon was to consolidate. During a long and severe bombardment of our consolidated positions this NCO by his coolness and energy set an excellent example to the men. All Platoon Officers were wounded, and Sergt McMahon ably consolidated his sector, and got into touch with the troops on our right. He showed great devotion to duty and from the commencement of the attack until our relief 60 hours later performed excellent work.'
Source: London Gazette
Date: 16 August 1917

Regimental number	6/3391
Address	Whangarei Hotel Whangarei
Marital status	Single
Next of kin	Mother, Mrs K Reinhardt, Karangahake Thames
Rank on embarkation	Private
Enlistment status	Volunteer
Unit name	New Zealand Expeditionary Force, 8th Reinforcements, Canterbury Infantry Battalion
Embarkation details	Unit embarked from Wellington on board Willochra on 13 November 1915
Medals	Military Medal 'Messines Offensive, 7th to 9th June 1917. During the attack on Messines the Officer in command of No 8 Platoon was severely wounded and Sergt McMahon took command of the platoon and ably led it to the line on which the Platoon was to consolidate. During a long and severe bombardment of our consolidated positions this NCO by his coolness and energy set an excellent example to the men. All Platoon Officers were wounded, and Sergt McMahon ably consolidated his sector, and got into touch with the troops on our right. He showed great devotion to duty and from the commencement of the attack until our relief 60 hours later performed excellent work.' Source: London Gazette Date: 16 August 1917
Miscellaneous details	Nominal Roll Vol. 1: Canterbury Infantry Batln/Eighth