Meaning : Battle in World War I (1917). An Allied offensive which eventually failed because tanks bogged down in the waterlogged soil of Flanders. Germans introduced mustard gas which interfered with the Allied artillery.

Meaning : Battle in World War I (1915). Germans wanted to try chlorine (a toxic yellow gas) as a weapon and succeeded in taking considerable territory from the Allied salient.

Meaning : Battle in World War I (1914). Heavy but indecisive fighting as the Allies and the Germans both tried to break through the lines of the others.