The tank. Though not wheeled, gas was also used for the first time in WWI.
The first tank was invented by the Brittish in the first world war 1914 - 1918 and used as a weapon in the battle of the somme in July 1916.
The Battle of the Somme, or Somme Offensive, occurred between July 1 and November 18, 1916. The importance of air power and the first use of the tank are noted.
A rock was probably the first weapon used
The Germans used the PanzerFaust (tank fist). It was a disposable anti tank weapon.
Atomic/nuclear weapons
Invented by French chemist Claude Berthollet, chlorine gas was first used as a weapon by the military during the first World War in 1914. Chlorine gas was first used as a disarming weapon, and later as a fatal poison.
chariot
The chariot was first used as a weapon by the Indo-Iranians from 1700 to 500 BCE. The chariot was built in eastern Europe.
It unknown who first used the phrase choose your weapon. The phrase us used quite often but the origins are not known. There just in not enough evidence for it.
sword
guns were used