Drawing on the vivid recollections of veterans of the First World War in the sound archives of the Imperial War Museums and the BBC, Dan Snow looks at the first German chlorine gas attacks of the war. During the 2nd Battle of Ypres in April and May 1915, poison gas was released on unsuspecting troops, and had a more powerful effect than even the German were expecting. From those who had to run away and those who managed to stay put in the trenches and keep firing, we hear what it was like to be there, and experience this new weapon.