This and earlier gas attacks , beginning Process_start at the Second Battle of Ypres ( 21 April – 25 May 1915 ) had given Giving the British time to replace Change_of_leadership improvised gas masks with effective mass-produced Manufacturing versions , obtain Getting other anti-gas equipment and to establish Building anti-gas procedures .

This and earlier gas attacks , beginning Process_start at the Second Battle of Ypres ( 21 April – 25 May 1915 ) had given Giving the British time to replace Change_of_leadership improvised gas masks with effective mass-produced Manufacturing versions , obtain Getting other anti-gas equipment and to establish Building anti-gas procedures .