Poisonous gas was used to subtly kill enemy soldiers crossing into defended territory. It was also formulated into hand grenades to be at the access of soldiers. It dramatically changed modern warfare because fighting tactics were now invisible and airborne, causing paranoia in traveling soldiers.
Machine guns were used to take down multiple enemies at one time without reloading. Automatic fire changed modern warfare permanently because soldiers no longer had to load each individual shot.
Tanks were used to travel through any terrain while bringing the power of heavy artillery missiles. This vehicle combined heavy firepower with incredible mobility, as well as rock hard walls to protect the driver of the tank.
Submarines were used as a method of transportation that was undetectable by enemy forces. Not only could submarines travel quickly and discretely, but they could also fire projectiles upward at enemy ships and forward at enemy subs.