From the end of World War II through the Korean War, the U.S. Army, the Chemical Corps and the U.S. Air Force made great strides in their biological warfare programs, especially concerning delivery systems. During the Korean War (1950–53) chemical soldiers had to again man the 4.2 inch chemical mortar for smoke and high explosive munitions delivery. During the war, the Pine Bluff Arsenal was opened and used for BW production, and research facilities were expanded at Fort Detrick. North Korea, the Soviet Union and China leveled accusations at the United States claiming the U.S. used biological agents during the Korean War; an assertion the U.S. government has denied. From 1952 until 1999 the Chemical Corps School was located at Fort McClellan.