When you reach the movable shell launcher and head up through the passageway to the next trench area, go left to collect this item from outside an abandoned nest.
"The Brodie helmet was also known as the Tommy or Shrapnel helmet and was worn by all British Empire forces, whether British, Canadian or Australian troops. Even the American army used it when they first joined the war. lts distinctive form brought it a whole host of other nicknames: dishpan hat, tin pan hat, washbasin, and battle bowler. The Germans called it the Salatschüssel (salad bowl)."