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 .

Even before the third test had been carried out Action , production of the old cores was halted Process_end , and all effort concentrated Aiming on the new Mark 4 nuclear bomb , which would become Becoming the first mass-produced nuclear weapon .