"The War Arrow! War Hut units train much more quickly."—In-game description
War Drums is a Big Button technology in Age of Empires III: The WarChiefs that is unique to the Sioux and can be researched at the War Hut once the Colonial Age is reached. Once researched, it reduces the train time of Cetan Bows and War Clubs by 33%, and Wakina Rifles by 25%.
War Drums is very important if the Sioux player is planning on using infantry.