<P> The first use of gas by the British was at the Battle of Loos, 25 September 1915, but the attempt was a disaster . Chlorine, codenamed Red Star, was the agent to be used (140 tons arrayed in 5,100 cylinders), and the attack was dependent on a favorable wind . However, on this occasion the wind proved fickle, and the gas either lingered in no man's land or, in places, blew back on the British trenches . This debacle was compounded when the gas could not be released from all the British canisters because the wrong turning keys were sent with them . Subsequent retaliatory German shelling hit some of those unused full cylinders, releasing more gas among the British troops . Exacerbating the situation were the primitive flannel gas masks distributed to the British . The masks got hot, and the small eye - pieces misted over, reducing visibility . Some of the troops lifted the masks to get some fresh air, causing them to be gassed . </P> <P> The deficiencies of chlorine were overcome with the introduction of phosgene, which was prepared by a group of French chemists led by Victor Grignard and first used by France in 1915 . Colourless and having an odor likened to "mouldy hay," phosgene was difficult to detect, making it a more effective weapon . Although phosgene was sometimes used on its own, it was more often used mixed with an equal volume of chlorine, with the chlorine helping to spread the denser phosgene . The Allies called this combination White Star after the marking painted on shells containing the mixture . </P> <P> Phosgene was a potent killing agent, deadlier than chlorine . It had a potential drawback in that some of the symptoms of exposure took 24 hours or more to manifest . This meant that the victims were initially still capable of putting up a fight; although this could also mean that apparently fit troops would be incapacitated by the effects of the gas on the following day . </P> <P> In the first combined chlorine--phosgene attack by Germany, against British troops at Wieltje near Ypres, Belgium on 19 December 1915, 88 tons of the gas were released from cylinders causing 1069 casualties and 69 deaths . The British P gas helmet, issued at the time, was impregnated with sodium phenolate and partially effective against phosgene . The modified PH Gas Helmet, which was impregnated with phenate hexamine and hexamethylene tetramine (urotropine) to improve the protection against phosgene, was issued in January 1916 . </P>

What types of weapons were used in world war 1