Technology during World War I

Infantry weapons for major powers were mainly bolt-action rifles, capable of firing ten or more rounds per minute. German soldiers carried Gewehr 98 rifle in 8mm mauser, the British carried the Short Magazine Lee–Enfield rifle, and the US military employed the M1903 Springfield and M1917 Enfield. Rifles with telescopic sights were used by snipers, and were first used by the Germans.

French machine gunners defend a ruined cathedral, late in the war

Machine guns were also used by great powers; both sides used the Maxim gun, a fully automatic belt-fed weapon, capable of long-term sustained use provided it was supplied to adequate amounts of ammunition and cooling water, and its French counterpart, the Hotchkiss M1914 machine gun.Their use in defense, combined with barbed wire obstacles, converted the expected mobile battlefield to a static one. The machine gun was useful in stationary battle but could not move easily through a battlefield, and therefore forced soldiers to face enemy machine guns without machine guns of their own.

Before the war, the French Army studied the question of a light machine gun but had made none for use. At the start of hostilities, France quickly turned an existing prototype (the "CS" for Chauchat and Sutter) into the lightweight Chauchat M1915 automatic rifle with a high rate of fire. Besides its use by the French, the first American units to arrive in France used it in 1917 and 1918. Hastily mass-manufactured under desperate wartime pressures, the weapon developed a reputation for unreliability.

Seeing the potential of such a weapon, the British Army adopted the American-designed Lewis gun chambered in .303 British. The Lewis gun was the first true light machine gun that could in theory be operated by one man, though in practice the bulky ammo pans required an entire section of men to keep the gun operating.  The Lewis Gun was also used for marching fire, notably by the Australian Corps in the July 1918 Battle of Hamel. To serve the same purpose, the German Army adopted the MG08/15 which was impractically heavy at 48.5 pounds (22 kg) counting the water for cooling and one magazine holding 100 rounds. In 1918 the M1918 Browning Automatic Rifle (BAR) was introduced in the US military, the weapon was an "automatic rifle" and like the Chauchat was designed with the concept of walking fire in mind. The tactic was to be employed under conditions of limited field of fire and poor visibility such as advancing through woods.

Early submachine guns were much used near the end of the war, such as the MP-18.

The US military deployed combat shotguns, commonly known as trench guns. American troops used Winchester Models 1897 and 1912 short-barreled pump action shotguns loaded with 6 rounds containing antimony hardened 00 buckshot to clear enemy trenches. Pump actions can be fired rapidly, simply by working the slide when the trigger is held down, and when fighting within a trench, the shorter shotgun could be rapidly turned and fired in the opposite direction along the trench axis. The shotguns prompted a diplomatic protest from Germany, claiming the shotguns caused excessive injury, and that any U.S. combatants found in possession of them would be subject to execution. The U.S. rejected the claims, and threatened reprisals in kind if any of its troops were executed for possession of a shotgun.

Grenades

German grenades from the First World War, Verdun Memorial, Fleury-devant-Douaumont, France

Grenades proved to be effective weapons in the trenches. When the war started, grenades were few and poor. Hand grenades were used and improved throughout the war. Contact fuzes became less common, replaced by time fuzes.

The British entered the war with the long-handled impact detonating "Grenade, Hand No 1". This was replaced by the No. 15 "Ball Grenade" to partially overcome some of its inadequacies. An improvised hand grenade was developed in Australia for use by ANZAC troops called the Double Cylinder "jam tin" which consisted of a tin filled with dynamite or guncotton, packed round with scrap metal or stones. To ignite, at the top of the tin there was a Bickford safety fuse connecting the detonator, which was lit by either the user, or a second person.

The "Mills bomb" (Grenade, Hand No. 5) was introduced in 1915 and would serve in its basic form in the British Army until the 1970s. Its improved fusing system relied on the soldier removing a pin and while holding down a lever on the side of the grenade. When the grenade was thrown the safety lever would automatically release, igniting the grenade's internal fuse which would burn down until the grenade detonated. The French would use the F1 defensive grenade.

The major grenades used in the beginning by the German Army were the impact-detonating "discus" or "oyster shell" bomb and the Mod 1913 black powder Kugelhandgranate with a friction-ignited time fuse. In 1915 Germany developed the much more effective Stielhandgranate, nicknamed "potato masher" for its shape, whose variants remained in use for decades; it used a timed fuse system similar to the Mills bomb.

Hand grenades were not the only attempt at projectile explosives for infantry. A rifle grenade was brought into the trenches to attack the enemy from a greater distance. The Hales rifle grenade got little attention from the British Army before the war began but, during the war, Germany showed great interest in this weapon. The resulting casualties for the Allies caused Britain to search for a new defense.

The Stokes mortar, a lightweight and very portable trench mortar with short tube and capable of indirect fire, was rapidly developed and widely imitated. Mechanical bomb throwers of lesser range were used in a similar fashion to fire upon the enemy from a safe distance within the trench.

The Sauterelle was a grenade launching Crossbow used before the Stokes mortar by French and British troops.