In six weeks during April and May 1915. as World War I escalated. Germany forever altered the way war would be fought. On April 22, at Ypres, German canisters spewed poison gas at French and Canadian soldiers in their trenches; on May 7, the German submarine U-20 without warning torpedoed the passenger ship Lusitania, killing 1198 civilians; and on May 31, a German zeppelin began the first aerial bombardment of London and its inhabitants. Each of these actions violated rules of war carefully agreed at the Hague Conventions of 1898 and 1907. Though Germany’s attempts to win the war quickly failed, the psychological damage caused by these attacks far outweighed the casualties. The era of weapons of mass destruction had dawned.