The Livens Projector was a simple mortar-like weapon that could throw large drums filled with flammable or toxic chemicals. In the First World War, the Livens Projector became the British Army's standard means of delivering gas attacks and it remained in its arsenal until the early years of the Second World War. It was created by the British army officer Captain William H. Livens of the Royal Engineers. Later, in World War II he worked on petroleum warfare weapons such as the flame fougasse and various other flame throwing weapons. A large calibre flame thrower, designed to engulf German trenches in burning oil, was deployed at the Somme in 1916. (One of these weapons was partially excavated recently by a British TV programme, having been buried as the tunnel in which it was being built took a direct hit from a German shell.) Prior to the invention of the Livens Projector, chemical weapons had been delivered either by "cloud attacks" or chemical-filled shells fired from howitzers. Cloud attacks at first were made by burying gas-filled cylinder tanks just beyond the parapet of the attacker's trenches and then opening valves on the tanks when the wind was right. (Later British practice was to bring up flatcars with gas cylinders on a line parallel to the front to be attacked, and open the cylinders without removing them from the rail car.) This allowed a useful amount of gas to be released but there was danger that the wind would change and the gas would drift back over the attacking troops. Chemical shells were much easier to direct at the enemy but could not deliver nearly as much gas as a cylinder tank.