Although very bulky at the time, a machine gunner could do the job of dozens of men with single rifles. With machine guns reinforcing massed rifle fire from the defending trenches, attackers were mowed down by the thousands before they could even get to the other side of “no-man’s-land.” Larger versions even served as anti-aircraft defense
Mustard gas and Chlorine gas were introduced. They ate at the skin and eyes and destroyed the lungs of anyone who breathed it in. Poison gas was used by both sides with devastating results (well, sometimes) during the Great War. The Germans pioneered the large-scale use of chemical weapons with a gas attack on Russian positions on January 31, 1915, during the Battle of Bolimov, but low temperatures froze the poison in the shells. The first successful use of chemical weapons occurred on April 22, 1915, near Ypres, when the Germans sprayed chlorine gas from large cylinders towards trenches held by French colonial troops. The defenders fled, but typically for the First World War, this didn’t yield a decisive result: the Germans were slow to follow up with infantry attacks, the gas dissipated, and the Allied defenses were restored. Before long, of course, the Allies were using poison gas too, and over the course of the war both sides resorted to increasingly insidious compounds to beat gas masks, another new invention; thus the overall result was a huge increase in misery for not much change in the strategic situation
Tanks were developed to protect soldiers against gunfire while advancing against the enemy. They were big and cumbersome but gave an obvious advantage.
Airplanes had been around for just a decade when WWI started, and while they had obvious potential for combat applications as an aerial platform for bombs and machine guns, it wasn’t quite clear how the latter would work, since the propeller blades got in the way. In the first attempt, the U.S. Army basically tied the gun to the plane (pointing towards the ground) with a leather strap, and it was operated by a gunner who sat beside the pilot. This was not ideal for aerial combat and inconvenient because it required two airmen to operate. Another solution was mounting the gun well above the pilot, so the bullets cleared the propeller blades, but this made it hard to aim. After the Swiss engineer Franz Schneider patented his idea for an interrupter gear in 1913, a finished version was presented by Dutch designer Anthony Fokker, whose “synchronizer,” centered on a cam attached to the propeller shaft, allowed a machine gun to fire between the blades of a spinning propeller.