World War One
Due to the massive amounts of ammunition capable of being fired per minute from machine guns of the time, Trench Warfare was a very costly method. Troops charging across No-Man's land were quickly cut down by even one machine gun. Both sides of the effort didn't have just one machine gun though; thus causing even heavier losses. The death toll was greater from machine guns than poison gas, but the guns were far quicker deaths and less of a pain. As well, the gunfire could be avoided by going into the dugout.
As stated above, the poisonous gas toll was not as severe as the gunfire, but was a far more gruesome death that usually wasn't able to be avoided. Gas bombs were dropped randomly without warning or during fighting periods. The main purpose of Gas bombing for Trench Warfare was to make advance easier and less painful for one side or the other. However, with both sides using the gas, the effects weren't as would be hoped.
Tanks, invented during the war as a means to combat the Trench Warfare and Gas Bomb fight style, were a new invention. With everything new improvements were to be made, but they did serve their purpose of coming away from the Trench Warfare, though not completely. The average tank was filled with ten men and carrying two machine guns.
The first flight run was done in 1903, in 1914 little had changed from the basics. Planes were initially used for spying, messenger systems, etc. However, later on they became far more advanced. The three category found nearing the end of World War 1 were Fighters, Bombers, and long-range bombers. All of these had great effect on the Trench Warfare style including gas bombing, air support against/for charges, and Trench bombing. In general the death total caused by Planes was relatively high, but wasn't until the later years of the war.