Static trench warfare developed in response to the perils of artillery and the power of rifles and machine guns. Despite the volume of industrial production devoted to manufacturing lethal weaponry, deeply-dug trenches in quiet sectors were not necessarily dangerous.

As long as the soldiers manning them were wary.

A watchful eye ensured that opposing troops were not sneaking in to attack; a patient rifleman could hinder the enemy’s ability to maneuver, attack or build defenses. Troops devised or adopted various methods to accomplish these tasks while keeping themselves out of harm’s way.

 
Trench warfare: a sniper wearing a French helmet stays safely hidden behind a parapet while hunting for targets with the help of a trench periscope, 1916.
Credit: Scientific American, May 6, 1916

The trench periscope was widely used, and could be made from simple materials such as two mirrors shown here, or could be manufactured by elegant optical manufacturers whose sales of opera glasses had declined. The sniper was as much a target as a lethal actor; the principles behind the contraption shown here were also used for machine guns.

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Our full archive of the war, called Scientific American Chronicles: World War I, has many articles from 1914–1918 on trench warfare in the First World War. It is available for purchase at www.scientificamerican.com/products/world-war-i/