concept, considering all gun-based weapons to be useless against modern aircraft. This belief was generally held by many forces, and the anti-aircraft role turned almost exclusively to missile systems. The Soviet Union remained an outlier, beginning the development of a new SPAAG in 1957, which emerged as the ZSU-23-4 in 1965. This system included search-and-track radars, fire control, and automatic gun-laying, greatly increasing its effectiveness against modern targets. The ZSU-23 proved very effective when used in concert with SAMs; the presence of SAMs forced aircraft to fly low to avoid their radars, placing them within range of the ZSUs. The success of the ZSU-23 led to a resurgence of SPAAG development. This was also prompted by the introduction of attack helicopters in the 1970s, which could hide behind terrain and then "pop up" for an attack lasting only a few tens of seconds; missiles were ineffective at low altitudes, while the helicopters would often be within range of the guns for a rapid counterattack. Notable among these later systems is the German Gepard, the first western SPAAG to offer performance equal to or better than the ZSU. This system was widely copied in various NATO forces. SPAAG development continues, with many modern examples often combining both guns and short-range missiles. Examples include the Soviet/Russian Tunguska-M1, which supplanted the ZSU-23 in service, the newer versions of the Gepard, the Chinese Type 95 SPAAA, and the British Marksman turret, which can be used on a wide variety of platforms. Some forces, like the US Army and USMC have mostly forgone self-propelled guns in favor of systems with short-range infrared-guided surface-to-air missiles in the AN/TWQ-1 Avenger and M6 Linebacker, which do not require radar to be accurate and are generally more reliable and cost-effective to field, though their ability to provide ground support is more limited. The U.S. Army did use the M163 VADS and developed the prototype design of the M247 Sergeant York. Present Day The wide spread usage of Unmanned Aerial Vehicles (UAVs or "drones") seems to bring back SPAAGs to most of the modern armies. These relatively cheap, low, slow and small targets are ideal for autocannons. Engaging these targets with expensive missiles is unsustainable on the long run, therefore SPAAGs are a much more economic way to counter the UAVs. These modern SPAAGs usually have short range missiles as well for longer range engagement. The Pantsir system from Russia