Jackson knew the most important resource in the state was the federal arsenal at St. Louis. There was only a small detachment of Union soldiers that guarded the arsenal and were under the command of Captain Lyon. But quietly, Lyon had sent almost all the gunpowder and weapons to safety in Illinois. Also, the United States Secretary of War, Simon Cameron, had sent a letter to Lyon authorizing him to raise more companies of Union soldiers. On May 6, Jackson sent his militia to camp near St. Louis in order to provoke the Union soldiers and perhaps secure their arms for his militia. However, on May 10, Lyon marched some 6,500 Union troops to surround the militia and arrest all of them. Following the Camp Jackson Affair, Lyon was promoted to Brigadier general and took charge of all Union forces in the state.