SALT LAKE CITY — The U.S. Army’s mistaken shipment of live anthrax samples to government and commercial laboratories occurred at a military post in a desolate stretch of the Utah desert that has been testing chemical weapons since it opened in 1942.

Though military officials say they were not aware of previous problems with anthrax, the Dugway Proving Ground, 85 miles west of Salt Lake City, has previously had at least two other problems with chemical weapons.

In 2011, Dugway was locked down for 12 hours because less than one-fourth of a teaspoon of VX nerve agent was unaccounted for. The agent affects the body’s ability to carry messages through the nerves.

Military officials launched an internal investigation, but the results were not released. Questions about that incident were not answered Thursday by military officials.