The UK was a signatory of the Hague Conventions (1899 and 1907) which outlawed the use of poison gas in warfare. However, during the First World War, in retaliation to the use of chlorine by Germany against British troops from April 1915 onwards, British forces deployed chlorine themselves for the first time during the Battle of Loos on 25 September 1915. By the end of the war, poison gas use had become widespread on both sides and by 1918 a quarter of artillery shells were filled with gas and Britain had produced around 25,400 tons of toxic chemicals.