St. Louis Arsenal
The St. Louis Arsenal is a large complex of military weapons and ammunition storage buildings owned by the United States Army in St. Louis, Missouri. During the American Civil War, the St. Louis arsenal's contents were seized and removed to Illinois by Union Captain Nathaniel Lyon, an act that helped fuel tension between secessionists and those citizens loyal to the Federal government.

Origin and early years of service
In 1827, the United States War Department decided to replace a 22-year old arsenal, Fort Belle Fontaine (located 15 miles (24 km) north of St. Louis on the bluffs above the Missouri River) with a larger facility to meet the needs of the rapidly growing military forces in the West. Lt. Martin Thomas selected a 37-acre (150,000 m 2) tract of land on a bluff overlooking the Mississippi River and procured the land for the new arsenal. It was close to the main military base, Jefferson Barracks, and had easy access to the city and the river. By 1840, 22 separate buildings had been erected, and a garrison of 30 ordnance soldiers manned the site, along with 30 civilian employees, who assembled finished weapons and artillery from parts supplied by private contractors and armories. In its original configuration it included Arsenal Island in the Mississippi River. The island has since disappeared. When the Mexican-American War erupted, the demand for small arms, ammunition, and artillery substantially increased. At its peak during the war years, the St. Louis Arsenal employed over 500 civilian workers. During the two years of war, the arsenal produced 19,500 artillery rounds, 8.4 million small arms cartridges, 13.7 million musket balls, 4.7 million rifle balls, 17 field cannon with full attachments, 15,700 stand of small arms, 4,600 edged weapons, and much more. Production was curtailed following the cessation of the war, although the arsenal workers (back to their normal complement of 30) did spend considerable time refurbishing and reconditioning surplus arms returned from the war. Another flurry of activity accompanied the Utah War in 1857”“58, when President James Buchanan ordered an expedition of Federal troops to suppress the Mormons. Employment exceeded 100 workers, and the arsenal provided much of the weaponry for William S. Harney's forces.

Civil War
Anticipating secession, a number of Southern states asked for their quota of arms and ammunitions to be shipped from the St. Louis Arsenal to state armories and aresenals. Buchanan's Secretary of War, John B. Floyd, a Virginian, was accused of aiding in this transfer of arms and resigned his post in December 1860 to return to Virginia. An investigation cleared him, but many suspected that his involvement had helped arm the Confederate States of America and prepare it for war in advance of actual ordinances of secession from the individual states. The armory, which was used for assembling weapons rather than manufacturing them, had the biggest collection of rifles and muskets of any of the slave states and was fourth after Massachusetts, District of Columbia, New York and California in total number of muskets and rifles (38,141). Despite its enormous strategic importance, it had traditionally been lightly guarded. In March 1861 the Missouri Constitutional Convention of 1861 voted 98 to 1 to stay in the Union but not supply weapons or men to either side if war broke out. The security of such a large munitions depot became an immediate flash point. On April 20, 1861 a pro-Confederate mob at Liberty, Missouri seized the only other arsenal in the state"the Liberty Arsenal and made off with about 1,000 rifles and muskets. On April 29 Union General Nathaniel Lyon seized the arsenal and sent all but 10,000 rifles and muskets to Illinois. Around May 1 Missouri Governor Claiborne Jackson who had favored the South but had stuck the neutrality posture called out the Missouri Militia for "maneuvers" about 4.5 miles (7.2 km) northwest of the arsenal at Lindell's Grove (now the campus of St. Louis University) then outside the city of St. Louis in what has been called "Camp Jackson." Lyon suspected the maneuvers were a thinly veiled attempt to seize the arsenal (suspicions furthered by the discovery that Jefferson Davis had sent artillery to the maneuvers). On May 10, Lyon surrounded the militia who surrendered. While parading them through the streets of St. Louis back towards the arsenal, a riot erupted. The troops opened fire on the crowd killing 28 and wounding 90 civilians outright and then killing another seven as the night progressed in what is called the Camp Jackson Affair. On May 11, the Missouri General Assembly approved a measure to create the Missouri State Guard to resist the Union invasion with Sterling Price as its major general. On May 12, Price and William S. Harney signed the Price-Harney Truce maintaining the earlier agreement to stay in the Union. On May 30, Harney was relieved of command by Abraham Lincoln for failing to deliver Missouri soldiers to the Union cause. On June 11, Lyon and Jackson failed to reach an agreement to deliver the troops which was to result in Lyon pursuing Jackson and the elected government across the state until evicting Jackson and installing a new governor. In the process Lyon was to be killed in the Battle of Wilson's Creek. The St. Louis Arsenal remained in Federal hands throughout the Civil War, and, with St. Louis firmly in Union control, provided substantial quantities of war materiel to the armies in the Western Theater.

Transfer to Jefferson Barracks
In March 1869, 10 acres (40,000 m 2) of the old arsenal grounds were given to the City of St. Louis for the creation of Lyon Park, named for Lyon. In 1871 the arsenal was transferred to the better secured Jefferson Barracks. That complex was retained by the U.S. Army, with substantial peaks in weaponry and ammunitions storage and dispensing during World Wars I and II. In 1956, it was transferred to the U.S. Air Force.

21st century
The arsenal complex remains an active part of the military today, with much of it off limits to tourists and visitors. The Arsenal is maintained by the USAF and the Department of Defense, housing a major branch of the National Geospatial-Intelligence Agency.