 At the outbreak of the Civil War, Lieutenant Benson was attached to the 2nd Artillery, Battery C, commanded by Brigadier General Lewis G. Arnold, posted at Fort Independence, Massachusetts.In January 1861, Arnold's command was transferred to Fort Jefferson, Florida to aid in the preparation for war following the secession of Florida from the Union.Benson was instrumental in assisting with the transfer of heavy artillery from Fort Taylor (under command of Captain John Milton Brannan) to arm Fort Jefferson—described by Arnold as "the key of the Gulf"— under the direction of Captain Montgomery C. Meigs.