Front-line trenches were not dug in straight lines. Otherwise, if the enemy had a successive offensive, and got into your trenches, they could shoot straight along the line. The French tended to build zig-zag trenches. However, the British Army preferred a system where each trench was dug with alternate fire-bays and traverses. Fire-bays were straight sections of trench where the troops did their shooting. Each fire-bay was protected at the side by a barrier of earth and sandbags.