3 weapons first used in ww1?

Tanks were first used in WWI. Zeppellins for observation and bombing. Poison gas as a weapon.

There are many other weapons that were widely used in WWI (and are often thought of as debuting there) but were not really used for the first time:

Fighter aircraft.

Machine guns.

Long-range (~100 km) artillery.

Hand grenades.

Flame throwers.

Submarines.