How did new technology used in world war i made it more deadly?

World War 1 was the first "War" that introduced new weapons into battle. When writing your short answer, think of the following points:
-The new use of Machine Guns
-Use of Flamethrowers
-Mortars and Artillery
-**POISON GAS** This is a key factor to write about.
-And Tanks/Aircraft/Submarines

All of the above made the war just as brutal and horrifying than previous ones. **Pro tip: Poisonous gas is best example to use. No cure (Excluding gas masks) and caused horrifying effects to humans.

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