Ground vehicles utilizing stealth technology have come to fruition at various times in history. The Challenger 2 features a redesigned hull and turret offering lower radar observability over its predecessor. More recently, the joint U.S./British Future Scout Cavalry System concept was experimented with and appeared in prototype form before being canceled. Other vehicles, particularly unmanned ground vehicles, may unintentionally have an undetectably low radar signature due to their small size. Various coatings and radar absorbing layers of material are available for combat vehicles. The Armored Gun System program of the 80's attempted to create a stealth vehicle. One of the competitors, the Stingray light tank later became Thailand's light tank. The M1A2 Abrams was also originally supposed