After the Virginia Secession Convention voted on April 17, 1861 to leave the Union, Virginia leaders began mobilizing forces to defend critical places including Manassas Junction, even before secession became official in a statewide referendum in May. Because Virginia had only a small militia, a newly created Army and Navy under Robert E. Lee had to build an army from scratch, aided by native citizens who had resigned from the United States Army. Camps of instruction soon appeared across the state to train recruits, and at Manassas, Camp Pickens became a major training ground where thousands of men from across Virginia and the South gathered despite having little military experience. Officers worked to turn farm boys, mechanics, and shop clerks into professional soldiers while the men also built earthworks around Manassas to protect the railroad junction. Large artillery pieces from the Gosport Navy Yard in Norfolk were installed in some of the forts, and although the weapons were formidable, the men had no experience using them, so volunteers from infantry units were trained to operate them. At Fort Mayfield, constant drilling in marching, handling weapons, loading men into an ambulance, and caring for the wounded steadily transformed young men and boys into professional soldiers during the war’s opening months.