In September 1916 a new weapon was employed for the first time at the battle of Flers-Courcelette. Which weapon was this?

In 1916 the war of attrition continued on the Western Front with several battles taking place. The Germans tried to dislodge the French from the fortress complex of Verdun, while the British tried to assist the embattled French by launching a massive frontal attack further west along the River Somme.