How was WWI so shockingly different from previous wars?
The advances in armament that became obvious as World War I got underway quickly showed that changes in tactics had not kept up with the changes in weapons. This was probably the biggest single area of difference between World War I and previous wars.
World War I saw the first large-scale use of airplanes by the military. Planes were used for reconnaissance, to drop bombs, and for attacks on ground forces.
German U-boats (submarines) marked the first widespsread use of submarines during a war, with devastating results in the first years.
Long-range artillery shelling and air-born delivery of bombs created the need for a completely new tactical approach to warfare - massed troops attacking each other by foot was no longer viable. Armored vehicles in the form of the first tanks came into use during World War I . Submachine guns and automatic rifles were also developed in response to the changed needs of the military during this war.
World War I was different from previous wars because it was fought at a far much larger scale than the wars fought before it. Furthermore, the war involved different countries from around the globe, with each providing arms and troops for participation. Consequently, the war resulted in one of the highest numbers of deaths of both soldiers and civilians.
8,528,831 - Total Military Deaths for all countries involved
In addition, the war introduced the use of chemicals (chlorine gas) to launch attacks, which led to the introduction of gas masks to fend off against such attacks. Moreover, the war saw improvements on weapon technology and defense systems, including body armor. The war registered the first use of flamethrowers and steel helmets. In addition, the World War I featured the first use of tanks and planes in the different battles.