As early as 1947 designers were asked to submit ideas for a new four engined bomber capable of having a top speed of 500 kts, reach an altitude of 50,000 ft, a range of 3000mi, and be capable of carrying a nuclear weapon. Two designs were chosen in case one of them failed. The aircraft had a crew of 5, and was resposible for maintaining Strategic Nuclear Deterrent during the early years of the Cold War. Under the Quick Reaction Alert System ( QRS ) the aircraft could be scrambled in minutes and the crews were on constant alert on operational readiness platforms.The Q R A was maintained until 1969 when the deterrent role was handed over to Polaris Submarines. As Soviet defenses improved, the aircraft was also fitted with various ECM devices. The aircraft was even used as a test bed for aircraft engines. This bomber also flew missions that covered 8000 miles, lasted 16 hours and necessitated numerous air to air refueling hookups. The aircraft also had a highly significant crew safety critisism and on a few occasions the testing of the brakes involved a situation that was unbelieveably controversial in the annals of aviation. Name this aircraft. Answer by PM only. Do not answer " Was It " or with a question mark. Just the name is sufficient. Answer will post on Saturday, 12 / 09 at 1100 hrs.