Poisonous gas was used to to affixate soldiers; they would breathe in this gas, choke on it, and die. This form of warfare allowed armies to battle each other without physically being there. For example, they could plant something far away from their trench that would release this poisonous gas when a soldier from the opposing army stepped on it. I belive that poisonous gas affected the morality of warfare by decreasing it; it allowed a more torturous death of opponents without actually witnessing it. The use of poisonous gas made it easier to keep more enemies away, but also made killing more amounts of people less difficult on a moral level, I believe.
The machine gun was used on opponents to slow down their advancing line of attackers. Machine guns could shoot hundreds of rounds of ammunition a minute and the standard military tactic during WW1 was the infantry charge. Casualties were huge. Many soldiers barely got out of their trench before they were cut down. The use of the the machine gun increased the amount of casualties to an appalling degree because it made killing vast amounts of soldiers very easy. I believe that the machine gun changed warfare by increasing the amount of casulaties.
The tank was an armored combat vehicle that moved on chain tracks, which allowed it to cross many types of terrain with ease. The tank allowed much more devastating destruction to be done unto the enemy. I believe that the tank did a great deal to end the horrors of trench warfare and brought back some mobility.
The submarine in WWI submerged themselves the same way as modern submarines. Sea water is allowed into a big tank in the hull, and pushes the air in the tank into a compression flask. To surface again, the engines or batteries have to turn a pump which repressurises the air in the flask to expand into the tank and push the water out again. I believe that the submarine allowed other countries to have a better chance at being a match for the British Navy during World War 1; for example, the Germans were able to destroy around hald of all the food and supplies transported by the British Merchant Navy with the use of submarines.
"Machine Guns." Machine Guns. History Learning Site, 2 Feb. 2009. Web. 13 Jan. 2015.
Fitzgerald, Gerard J. "Warfare and Medical Response During World War I." American Journal of Public Health. American Public Health Association, July 2008. Web. 14 Jan. 2015.