US Navy doctrine stressed long-range air cover to counter both high-speed aircraft and missiles, and development of newer short range defenses had been largely ignored. While the Navy was developing expensive long-range fighters like the Douglas F6D Missileer, most ships were left with older weapons, typically Bofors 40 mm guns or Oerlikon 20 mm cannons. By the early 1960s their capability against modern aircraft and missiles was limited; a lack of fast-reacting mounts, gunsight radars of limited accuracy, and long settling times for the fire control systems all meant that the guns were unlikely to be able to respond effectively against high-speed aircraft.