By 1957, the US Air Force began to phase out the B-47. The Stratojet's structure proved prone to metal fatigue, and the air- craft was unable to meet the SAC requirement that one-third of the planes always be ready for takeoff with only 15 minute's notice. Boeing had also introduced the B-52. Just as in the previous century, when the power of England's Royal Navy had created the Pax Britannica, the might of SAC's B-47s had provided a Pax Americana during the early years of the Cold War. Although the United States' B-47 fleet was an armed force of unparalleled power, the planes never dropped a weapon in anger.
