What warfare changes happened in World War 1?

As with any major war, there were many firsts and many innovations. Perhaps the most dramatic IMO was the German combined arms effort. Of course, combined arms had been around for centuries, but the German combination of mobile armored formations, fast moving infantry, ground support air craft, commandos, artillery, paratroopers, etc. was an immense step up and made the German military the most efficient the world had ever seen. Modern armies such as the US Army are modeled on this concept. At sea the first true submarines were manufactured, again a German innovation. There had been subs before for about 150 years, but they were all really just surface ships that could temporily go under water. These possibly war winning machines had been invented by 1940 but were ignored for production until mid 1944. Also at sea were the massive air craft carrier ships. These were largely the innovations of the Japanese and American fleet commanders. The British had some AC too, but their leadership in the field was lacking as they mainly used their ships for tactical combat. The American/Japanese fleets both used them for the much more important strategic role, where they were used to gain control of vast areas of sea/land areas. They are still used in this capacity today by the Americans. Coming late in the war and only used in one theatre, were the atomic weapons. They obviously did alter the last few weeks of the war's course between Japan and the USA, but otherwise had little effect on the overall course of WWII. It is interesting too the weapons that were not used........IMO the major one being the huge German stockpile of chemical weapons which included about half the world supply including vast amounts of nerve gas. These were never used or even deployed that I know of. The USA also had some of these weapons and had begun stockpiling them in the Italian area in 1944 presumably to be used against German forces. To my knowledge they never were.