U.S. B-57 Canberras were primarily used for dive bombing and strafing, with the early models mounting eight .50 caliber machine guns, four per wing. Later models mounted four 20mm cannons, two per wing, for strafing. These weapons combined with their bomb loads and four hours of flight time made them excellent ground support aircraft, as well as exceptional truck killers along the Ho Chi Minh trail. Deployed along the notorious "trail" for much of their eight years in Vietnam, Canberras participated in truck hunting campaigns during operations Barrel Roll, Steel Tiger, and "Tiger Hound", gaining reputations with their "Centurion Club" which consisted of Canberra crews which attained 100 truck kills.