How did weapons such as the airplane, bayonet, poison gas, and u-boats make World War I more deadly than previous wars?
World War I is often considered the first modern war. New weapons of combat were utilized to created unprecedented casualties. Airplanes were a popular weapon in the newspapers and on the radio. Papers told the tales of "dogfights" in the air and exalted the ace pilots with the most victories. Airplanes were used to bomb enemy locations with deadly effect. The more practical and successful utilization of aviation was in the area of gathering intelligence. When one side can easily track the locations of its enemies, the body counts will escalate.
Poison gas had two effects on the war. While not killing very many soldiers, it did have the effect of creating mass casualties. Soldiers could become sick enough from gas poisoning to have to be removed from the front lines until they recovered. Casualties were just as harmful to the war effort as deaths. Poison gas also had a dramatic psychological effect on soldiers. Infantryman would think they were sick from poison gas, when actually, they were just suffering from a common cold. The fear of gas attacks affected the strategies of both sides in a way that caused more death.
The u-boats, or submarines as they are called today, were also deadly for two reasons. First, it could be used to establish a blockade to starve out the enemy population. Secondly, the submarine was very effective at destroying battleships through the use of torpedoes.
Bayonets could be used to kill people from a distance through the use of ammunition, but could also be used to kill in hand-to-hand combat.