of only 17 Roman Catholic priests to do so. He was commissioned as a Chaplain to the Forces, 4th Class (equivalent to a Captain) in the Army Chaplains' Department on 18 November 1914 and joined the 2nd battalion, Royal Munster Fusiliers who were already in action on the Western Front in France. The battalion, pre-war regular troops who formed part of the 3rd Infantry Brigade of the 1st Division, were amongst the first British troops to be deployed to France. The unit had fought at the Battle of Mons and after Gleeson joined them they participated in the First Battle of Ypres (Octonber-November 1914). British officer and poet Robert Graves recalled in his autobiography Good-Bye to All That that during this battle Gleeson found himself the only unwounded officer of the battalion and, having removed his chaplain's insignia that indicated his non-combatant status, took command of the unit and held until relieved. In December he joined the battalion in a counterattack at the Battle of Givenchy. That month he wrote critically of those in Britain who supported the war, stating "If ... advocates of war were made to be soaked and caked and crusted with cold, wet trench mud, like these poor soldiers, and to wear those mud-weighted coats, they would not be so glib with their treatises on the art of war. These militants should be made to undergo a few nights in cheerless billets [and] mud-river trenches to teach them a lesson. What is it all for at all?". On Christmas Day the 2nd Munsters were in part of the front line unaffected by the Christmas Truce and Gleeson chose to conduct a Mass in one of the front line trenches that was frequently under fire. The mass was in memory of the seven officers and 200 men of the Munsters who had died in an action at Festubert from 21–22 December. The 2nd Munsters, barely recovered from their earlier losses, were ordered to halt a German advance that had already captured the front line trenches of an Indian unit. The men held out for 60 hours, including what Gleeson called a "dreadful night of carnage", before being relieved. Gleeson noted in his diary that day "such desolation. Such suffering! If all militarists had hearts at all they should bleed, if they saw the scene of frozen men I aw today - this Chrismas day of 1914 AD.