The Action called the Hairpin in which Mervyn was fatally wounded

The Regimental History published soon after the War describes the events in the Hairpin on 20/21 December 1915.
“But the tragedy of the Hairpin came on the night of 20th December, when the Battalion was ordered to send all its bombers, together with some bayonet men from “B” Company, over the top on the right of the Hairpin to jump into the German trench and bomb along it, while a party from the 7th Battalion restored a barricade (in the German front line adjoining the afore-mentioned captured strip of 50 yards) which the Germans had rushed early that morning.
The attack was most gallantly  led by the Battalion Bombing Officer, 2nd Lieutenant A.M.Thompson, an officer of the the 14th Royal Fusiliers, attached to Civil Service Rifles, but from the outset there was not the slightest chance of success.
However, 2nd Lieutenant Thompson and the N.C.Os and men with him went to their end unflinchingly, and though the enemy put down an impenetrable barrier of bombs, rifle grenades and machine gun bullets, the tragic scheme went on until all officers and N.C.Os taking part had been put out of action.
There were many most valuable lives lost on that night unfortunately, as it turned out, to no purpose for the Germans a few days later blew up the whole trench and a number of the 23rd London Regiment who were holding it went with it.