Poisonous Gas was the most popular weapon used in World War One. The French were The forts people to use gas as a weapon and threw tear gas bombs at their enemies. Without gas masks, poisonous gas was able to kill many soldiers. Poisonous gas was efficient for killing in WW1 because soldiers were able to kill other soldiers from farther away and unlike bullets, gas was able to kill several soldiers at once.
Machine Guns in WW1 were able to shoot 100 bullets a minute. This enabled soldiers to kill many soldiers at one time from a distance. However, when soldiers peaked their heads of of their trenches to shoot machine guns, there was a high possibility of being shot because snipers were always looking for heads popping out.
The tank was first introduced in World War One at the Battle of Flers. Tanks were originally very slow moving. However, tanks made easier and safer transportation for soldiers during Trench Warfare.
The first submarines were called U-Boats. U-Boats were valuable for war at sea because they were able to sneak up on boats and sink them from underwater.