B1

Design studies
The first post-B-70 study was known as the Subsonic Low Altitude Bomber (SLAB), which was completed in 1961. This was followed by the similar Extended Range Strike Aircraft (ERSA), which added a Variable-sweep wing planform, something then very much in vogue in the aviation industry.[11] ERSA envisioned a relatively small aircraft with a 10,000 lb (4,500 kg) load and a range of 8,750 nautical miles (16,200 km), with 2,500 nmi (4,600 km) being flown at low altitudes. In August 1963 the similar Low-Altitude Manned Penetrator (LAMP) design was completed, which called for an aircraft with a 20,000 lb (9,000 kg) load and somewhat shorter range of 7,150 nautical miles (13,200 km).

These all culminated in the October 1963 Advanced Manned Precision Strike System (AMPSS), which led to industry studies at Boeing, General Dynamics, and North American. In mid-1964, the USAF had revised its requirements and retitled the project as Advanced Manned Strategic Aircraft (AMSA), which differed from AMPSS primarily in that it also demanded a high-speed high-altitude capability, albeit slower than the Valkyrie at about Mach 2.[2] Given the lengthy series of design studies, Rockwell engineers joked that the new name actually stood for "America's Most Studied Aircraft".[12]


[edit] First cancellation
The cancellation of the B-70 project had led some to question the need for a new strategic bomber at all. The Air Force was adamant about retaining bombers as part of the nuclear triad concept that included bombers, SLBMs, and ICBMs in a combined package that complicated any potential defense. The arguments for keeping the bombers, however, were hotly debated. The original argument was that the bombers could be kept in the air during times of increased defensive posture, where they would be difficult to attack. Missiles of the era, like the Atlas and Redstone, required a lengthy fuelling procedure immediately before launch, and were therefore vulnerable to air attack while still on the ground. They also had low accuracy; enough to attack cities as a strategic deterrent, but not enough to attack hardened military targets. To attack these targets, the bombers were required.

In the early 1960s newer generations of missiles with solid rocket motors were being introduced that could be launched quickly, even faster than bombers, and were sited in underground silos for protection. Sneak attacks on these weapons would be very difficult for the USSR, which lacked the required accuracy in their own weapons and would have to use their bombers in order to be effective against them. US air defenses would have made such an attack extremely unlikely to succeed. Accuracy of the new weapons was so improved that direct attacks against similar weapons in the USSR were a real possibility, and attacks on other military bases were now possible. Making matters more troublesome for the Air Force was the introduction and rapid improvement of the U.S. Navy's SLBM force, which had considerably better survivability than either bombers or hardened missile silos. After this period the Air Force used a number of different arguments to make its case for the strategic bomber, including the conventional role and "recall-ability", but these arguments were much less convincing.

One of the biggest critics of the bomber portion of the triad was Secretary of Defense Robert McNamara who preferred ICBMs over bombers for the Air Force side of the deterrent force. In testimony before Congress, McNamara said, "The strategic missile forces for 1967-71 will provide more force than is required for 'Assured Destruction' ... a new advanced strategic aircraft does not at this time appear justified."[13] His opposition led to the AMSA program being stopped in 1964.[11] The program was revived only a few years later however, and in 1968 an advanced development contract was issued to IBM and North American Rockwell. McNamara remained opposed to the program in favor of upgrading the existing B-52 fleet, and adding just under 300 FB-111s for shorter range roles then being filled by the B-58. He vetoed the AMSA program and canceled it once again.[11]


[edit] B-1A program

A B-1A in flight showing its underside, 1981.President Richard Nixon re-established the program after taking office, in keeping with his administration's flexible response strategy that required a broad range of options short of general nuclear war.[13] Secretary of Defense Melvin Laird reviewed the programs and decided to lower the numbers of FB-111s, claiming it lacked the required range, and recommended that the AMSA design studies be accelerated. In April 1969 the program officially became the B-1A. This was the first entry in the new bomber designation series, first created in 1962.

After the prolonged development period, the production contract was finally awarded in 1970. The original program called for two test airframes, five flyable aircraft, and 40 engines. This was cut in 1971 to one ground- and three flight test aircraft (74-0158 through 0160). First flight was set for April 1974. The company changed its name to Rockwell International and named its aircraft division North American Aircraft Operations in 1973.[14] A fourth prototype (76-1074) was ordered in the FY 1976 budget. This fourth aircraft was to be built to production standards. At one time, some 240 B-1As planned to be built, with initial operational capability set for 1979.[11]

Rockwell's design featured a number of features common to 1960s U.S. designs. These included the use of variable-sweep wings in order to provide both high lift during takeoff and landing, and low drag during a high-speed dash phase. With the wings set to their widest position the aircraft had considerably better lift and power than the B-52, allowing it to operate from a much wider variety of bases. Penetration of the USSR's defenses would take place in a dash, crossing them as quickly as possible before entering into the less defended "heartland" where speeds could be reduced again. The large size and fuel capacity of the design would allow this dash portion of the flight to be relatively long.


USAF Rockwell B-1B Lancer arrives at RIAT 2008In order to achieve the required Mach 2 performance at high altitudes, the air intake inlets were variable. In addition, the exhaust nozzles were fully variable. Initially, it had been expected that a Mach 1.2 performance could be achieved at low altitude, which required that titanium be used in critical areas in the fuselage and wing structure. However, this low altitude performance requirement was lowered to only Mach 0.85, reducing the amount of titanium, and the overall cost.

Crew escape was provided for using an escape pod that ejected a portion of the entire cockpit with both pilots inside, as opposed to the more conventional ejection seats; it was felt that egress during a high-speed, high-altitude dash would be too dangerous without pressurization. A pair of small canards mounted near the nose are part of an active vibration damping system that smooths out the otherwise bumpy low-altitude ride, reducing crew fatigue and improving airframe life.

An extensive suite of electronics was planned, including a Litton LN-15 inertial navigation system, a Doppler radar altimeter, a Hughes forward-looking infrared, a General Electric APQ-114 forward-looking radar and a Texas Instruments APQ-146 terrain-following radar. The terrain-following radar, in particular, would allow the B-1 to fly at much lower altitudes during the "dash" phase of the mission than the B-52, which relied on older systems that demanded higher minimum altitudes during bad weather.

Overall it had a range similar to that of the B-52, although more of the flight could be low-level. A combination of flying lower due to better navigation systems and a greatly reduced radar cross section made it much safer from attack by missiles, and the latter also improved its odds against fighters as well. In situations where fighters were the expected competition (i.e. outside the USSR), its high-speed dash was a potentially useful technique the B-52 could not match. A convincing B-52 replacement had arrived.