Source: Earned the Military Medal for “Bravery in the Field” during the actions at the Somme September 1916.
Duty Nobly Done describes an action in which Private David Egan was involved:
In the interlude between the two stages of the barrage, the Germans attempted a spoiling attach on the positions of the 18th and 20th Battalions. A few of them managed to reach the jumping off trench before Lieutenant Hugh Sykes and some of the 18th Battalion men with help from Lieutenant Gidley and some bombers of the 19th, in support of the two forward battalions, drove them off. In one case, Private David Egan picked up a Lewis gun and moved out of the trench [during the September 15, 1916 attack at the Somme] to a position from which he could enfilade the attacking Germans, causing many casualties among them and forcing the survivors to withdraw.
Antal, S., & Shackleton, K. (2006). Courcelette: Taking a Turn On the Somme. In Duty nobly done: The official history of the Essex and Kent Scottish Regiment (1st ed., p. 211). Windsor, ON: Walkerville Pub.