World War I - British troops adavance on German African soldiers during the Battle of Loos was the largest British offensive mounted on the Western Front in 1915 during World War I. The first British use of poison gas occurred and the battle was the first mass engagement of New Army units. Prior to the British attack, about 140 long tons of chlorine gas was released, with mixed success; in places the gas was blown back onto British trenches. Due to the inefficiency of the contemporary gas masks, many soldiers removed them as they could not see through the fogged-up talc eyepieces or could barely breathe with them on..