Mightier Than the Shovel Achievement and Trophy Guide
(Find the hidden Cavalry Sword and take down an enemy on the French countryside in the campaign)
War Story: Through Mud and Blood
Start the mission “Breakdown” and make your way into the little town straight ahead. Turn left and you can see a house with open windows and the lights on.
Inside you can find the Cavalry Sword on the floor. Pick it up and use it on the enemy upstairs and you unlock the achievement / trophy.