 When the Civil War erupted Dyer stayed with the Union, and in August 1861 he was given command of the Springfield Armory in Springfield, Massachusetts, where his expansions and enlargement of operations gained notice.During his tenure at Springfield, Dyer was responsible for expanding the output of small arms for the Union Army.Doubts about the wisdom of placing a southerner in such a position of responsibility were rapidly dispelled as Dyer upgraded production with energy and dispatch.