On 11 July 1917, during "Unternehmen Strandfest" (Operation Beachparty) at Nieuport on the coast, the Germans introduced a new weapon into the war when they fired a powerful blistering agent Sulfur mustard (Yellow Cross) gas. The artillery deployment allowed heavy concentrations of the gas to be used on selected targets. Mustard gas was persistent and could contaminate an area for days, denying it to the British, an additional demoralising factor. The Allies increased production of gas for chemical warfare but took until late 1918 to copy the Germans and begin using mustard gas.