The M-1939, manufactured by the Soviet Union and sold to client states such as North Vietnam, was captured in the A Shau Valley during the Vietnam War by C/2-7 Cavalry of the 1st Cavalry Division in August 1968 and was located at Camp Evans when the 101st Airborne Division (Airmobile) arrived; it was a Russian copy of the pre-World War II Swedish-made Bofors L-60. The Communist Chinese version was known as the M-55. The ZPU-4, first produced in 1949 by the Soviet Union, was used against U.S. forces in Korea, Vietnam, Iraq, and Afghanistan and remained an effective air defense weapon against low-flying aircraft, especially lethal to American helicopters during the Vietnam War; this weapon was captured by the 101st Airborne Division (Air Assault) during Operation Desert Storm. The ZSU-23, manufactured by the Soviet Union and sold to client states such as North Vietnam, was captured during the Vietnam War by 1-327th Infantry of the 101st Airborne Division (Airmobile) in August 1968; this towed version of the ZSU-23-4 armored, self-propelled gun was an effective air defense weapon against low-flying aircraft, especially helicopters. The M-1939 had 2 barrels, a maximum range of 5,330 yards, a rate of fire of 170 rounds per minute, and weighed 2,495 pounds; the ZPU-4 had 4 barrels, a maximum range of 8,749 yards, a rate of fire of 600 rounds per minute, and weighed 3,990 pounds; and the ZSU-23 had 2 barrels, a maximum range of 3,520 yards, a rate of fire of 2,000 rounds per minute, and weighed 2,094 pounds.