During Operations Linebacker and Linebacker II during the Vietnam War, the term was used as a nickname for the long lines of Boeing B-52 Stratofortress aircraft as they approached their targets. Although the tight groupings were necessary for electronic warfare, their paths were predictable and they were slow targets for North Vietnamese surface-to-air missiles. Within two weeks, the Air Force altered its tactics and began to vary the incoming paths of bombers. In addition to changing this aspect of the attack, the bombers were told to take longer turns after discharging their load, instead of the sharp turn which gave them greater radar exposure. The practice is also used by some aerobatic teams, particularly those associated with a military branch such as the Blue Angels or Thunderbirds of the United States and Canada's Snowbirds, with the teams' aircraft taxiing in tight formation to the runway and maintaining such grouping during takeoff.