to the best extant records, up to 25,000 Marylanders went south to fight for the Confederacy. About 60,000 Marylanders served in all branches of the Union military. Many of the Union troops were said to enlist on the promise of home garrison duty. Maryland's naval contribution, the relatively new sloop-of-war USS Constellation was flagship of the US Africa Squadron from 1859 to 1861 and continued in this role during the war. In this period, she disrupted the African slave trade by interdicting three slave ships and releasing the imprisoned slaves. The last of the ships was captured at the outbreak of the Civil War: Constellation overpowered the slaver brig Triton in African coastal waters. Constellation spent much of the war as a deterrent to Confederate cruisers and commerce raiders in the Mediterranean Sea. Occupation of Baltimore A Union artillery garrison was placed on Federal Hill with express orders to destroy the city should Southern sympathizers overwhelm law and order there. Following the riot of 1861, Union troops under the command of General Benjamin F. Butler occupied the hill in the middle of the night. Butler and his troops erected a small fort, with cannon pointing towards the central business district. Their goal was to guarantee the allegiance of the city and the state of Maryland to the federal government under threat of force. This fort and the Union occupation persisted for the duration of the Civil War. A large flag, a few cannon, and a small Grand Army of the Republic monument remain to testify to this period of the hill's history. Because Maryland remained in the Union, it fell outside the scope of the Emancipation Proclamation. A constitutional convention in 1864 culminated in the passage of a new state constitution on November 1 of that year. Article 24 of that document outlawed the practice of slavery. A campaign by state politician John Pendleton Kennedy and others ensured that abolishment of slavery would be in the new document, and the issue was hotly contested for nearly a year throughout the state. In the end the elimination of slavery was approved by a 1,000-vote margin. The right to vote was extended to non-white males in the Maryland Constitution of 1867, which is still in effect today. The war on Maryland soil The largest and most significant battle fought in the state was the Battle of Antietam, fought on September 17, 1862,