April 22- May 5 Second Battle of Ypres. Chemical weapons used for the first time. (8h 8min, apr 22, 1915 y – 23h 35min, may 5, 1915 y)
Added to timeline:
Date:
8h 8min, apr 22, 1915 y
23h 35min, may 5, 1915 y
~ 13 days