Watch this American Rifleman Television video segment 'Over There! Part 8' to learn about the role of American snipers in World War I, the use of "trench gun" shotguns and the end of World War I.
Before sniping could make an impact on the battlefield, two things were required: accurate rifles and optical sights.
Against one or two of the enemy, mortar fire is is ineffective. The military's answer to the problem is snipers.