The 1st Massachusetts Battery was one of the Massachusetts militia units which responded to President Abraham Lincoln's call for 75,000 volunteer troops to serve a term of 90 days at the start of the war. Due to the fact that these first units were en route to Washington on April 19 (the anniversary of the Battles of Lexington and Concord), in Massachusetts these 90 day troops are often known as the "Minutemen of '61." The battery was organized for active duty on April 20 though it was not mustered into federal service until May 18 near Baltimore, Maryland. The battery left Massachusetts for Fort Monroe, Virginia on April 21, 1861 and arrived on April 23. From there they moved to the Naval Academy in Annapolis, Maryland and were quartered there until May 4. They were assigned to garrison a key railroad relay station 15 miles outside of Baltimore in Elkridge, Maryland. Here they were officially mustered into United States service. They later moved to Camp Clare near Baltimore and then were stationed at Monument Square in Baltimore where they served garrison duty until August 2. On that date they were mustered out and returned home to Massachusetts.