The Southwestern Proving Ground Building No. 4 is a gun shelter and stockade at 259 Hempstead County Road 279 in Oakhaven, Arkansas, northwest of the city of Hope. It is located on property that was once part of the Southwestern Proving Ground, a major military facility during World War II whose largest portion was transformed into Hope Municipal Airport. Building No. 4 is a roofless concrete structure with seven bays open to the southeast, with smaller openings on the northwest side. It was built in 1941 to replicate typical stockaded gun placements in field conditions, its two-foot-thick walls designed to isolate gun crews from the dangers of fire and exploding ammunition. The building is now used by a private owner for storage and agricultural purposes.