This thesis is an historical analysis of the amphibious operations of the 46th Indiana. The primary research question is whether the amphibious operations of the 46th Indiana were effective towards the Union’s success in the Mississippi River valley. Using Marine Corps Doctrinal Publication 1-3, Tactics, this thesis will compare the 46th Indiana’s employment of tactics to the Marine Corps’ current use of tactics according to doctrine. Tactical concepts that achieve success on the battlefield are achieving a decision, gaining an advantage, being faster, adapting, cooperating, and exploiting success. These six concepts form the foundation of the analysis of the 46th Indiana’s operations and tactics during the Civil War. Secondary research areas to determine the effectiveness of the 46th Indiana’s amphibious operations are training, command and control, casualty statistics, unit cohesion and morale.