This dissertation provides analysis on several areas of study related to the history of the United States Marine Corps in the Civil War Era. One element scrutinizes the efforts of Commandant Archibald Henderson to transform the Corps into a more nimble and professional organization. Henderson's initiatives are placed within the framework of the several fundamental changes that the U.S. Navy was undergoing as it worked to experiment with, acquire, and incorporate new naval technologies into its own operational concept. Analysis of the strengths and weaknesses of Henderson's programs are provided and comparisons drawn with those priorities established by his successor, Commandant John Harris. In addition, the operations undertaken by the Corps during the Civil War are evaluated in terms of their relative benefit for the national military establishment as a whole. The Corps organization and operational concept is scrutinized and compared with that of similar military structures. In particular, the relationship between the U.S. Marine Corps and the Confederate States Marine Corps are compared. In the process, the South's Corps, born in part out of that of the North's, exhibited many distinct advantages that the USMC solidly resisted adopting during the war years. The influence of key leaders, both military and civilian, reveals many problems that continued to negatively affect the Corps' ability to meet operational requirements as defined by senior naval and Army commanders. Yet despite these issues, the Corps' Civil War experiences served as a crucible for forging a new generation of leaders who earnestly fought for reforms and increased professionalization of the unit. Although the Corps suffered from several problems related to lack of institutional vision and leadership failings of some senior officers, at a small unit level the officers and Marines performed their duties in a competent, enthusiastic, and courageous manner. Therefore, Marines continued to be in great demand by naval commanders at all levels, who actively sought their service in a variety of operation.