Trench warfare
Trench warfare has become archetypically associated with the First World War of 1914–1918, when the Race to the Sea rapidly expanded trench use on the Western Front starting in September 1914. By the end of October 1914 the whole front in Belgium and France had solidified into lines of trenches, which lasted until the last weeks of the war. Mass infantry assaults were futile in the face of artillery fire as well as rapid rifle and machine-gun fire. Both sides concentrated on breaking up enemy attacks and on protecting their own troops by digging deep into the ground. Trench warfare also took place on other fronts, including in Italy and at Gallipoli.
John T. Thompson
World War I began in Europe in 1914, and Thompson was sympathetic to the Allied cause. Since the U.S. did not immediately enter the war, and because he recognized a significant need for small arms in Europe (as well as an opportunity to make a substantial profit), Thompson retired from the Army in November of that year and took a job as Chief Engineer of the Remington Arms Company. While with the company he supervised the construction of the Eddystone Plant in Chester, Pennsylvania, at that time the largest small arms plant in the world. It manufactured Pattern 1914 Enfield rifles for British forces, and Mosin–Nagant rifles for Russia.
The introduction of trench warfare in the First World War changed tactics substantially, and by 1916 Thompson was experimenting again with automatic small arms, this time attempting to design a weapon that troops could use to clear an enemy trench—what he called a "trench broom." Thompson studied several designs and was impressed with a delayed-blowback breech system designed by John Blish, a commander in the United States Navy. With Blish as a partner, Thompson obtained the necessary venture capital to form the Auto-Ordnance Company, and began working on the design of what eventually became the Thompson submachine gun.