This photograph from World War 1 shows a French artillery unit struggling to emplace their gun in the soft mud of the Western front. Note the very deep ruts around the gun crew where the cannons have sunk into the mud and been dragged. It required an incredible amount of effort to move men and equipment through the slippery mud of the front lines.
The Allies often quipped that the greatest weapon in the German arsenal was the rain and the mud. Incessant rain plagued the western front and turned the trenches into rivers.