Question

what is
corporal turnbull

Answer 1

Corporal Turnbull had come to give a lecture on hand-grenade. He'd come back from Dunkirk (France).

Answer 2

Corporal Turnbull was a strong and sturdy man. He was boastful of his physical toughness. He had come back from Dunkrik. He was tough, serious and even revengeful. He did not take Private Quelch's interruption lightly and took a sort of revenge on him by sending him to kitchen to do cooking duties.