In the Springspring and Summersummer of [[1915]] he undertook the organisation and leadership of special voluntary recruiting campaigns in Cork, Limerick and [[County Clare|Clare]]. While opposing any question of [[conscription]], he said he was not asking the people to do anything or take any risks he was not prepared to share himself. Receiving Captaincy and Company command in July 1915, he served with his battalion on the [[Somme]], contributing from early [[1916]] a series of widely quoted articles from the trenches to the London ''[[Daily Express]]'' and the ''[[Irish Times]]''.
Deafness by shellfire and ill-health necessitatesnecessitated his transfer to the 3rd. reserve battalion,. [[General Hickie]] commentingcommented "he has done really well in the trenches". AppliesSheehan applied to be decommissioned in Autumn 1916, but General Maxwell decidingdecided on his retention. BetweenHe periodswas ofhospitalised hospitalisation,often. limitedA recruitingrenewed toapplication helpin those Irish at the front lacking rearguard support. Renewed application Autumnautumn [[1917]] to be decommissioned iswas accepted,. The bulletin readingread: "relinquished his commission on account of ill-health contracted on active service, and is granted the honorary rank of Captain, 13 January, [[1918]]".
