In 1955, the USAF issued requirements for a new bomber combining the payload and range of the
Boeing B-52 Stratofortress with the Mach 2 maximum speed of the
Convair B-58 Hustler.
 In December 1957, the USAF selected
North American Aviation's
B-70 Valkyrie for this role.
 The Valkyrie was a six-engine bomber that could cruise at
Mach 3 at high altitude (70,000 ft or 21,000 m).
interceptor aircraft, the only effective anti-bomber weapon in the 1950s,
 were already unable to intercept the high-flying
 the Valkyrie would fly at similar altitudes, but much higher speeds, and was expected to fly right by the fighters.
The XB-70 Valkyrie was chosen in 1957 to replace the B-58 Hustler, but suffered as a result of a switch in doctrine from high to low-altitude flying profiles
By the late 1950s, however, antiaircraft
surface-to-air missiles (SAMs) could threaten high-altitude aircraft,
 as demonstrated by the
1960 downing of
Gary Powers' U-2.
 The USAF Strategic Air Command (SAC) was aware of these developments and had begun moving its bombers to low-level penetration even before the U-2 downing. This tactic greatly reduces radar detection distances through the use of
terrain masking; using features of the terrain like hills and valleys, the line-of-sight from the radar to the bomber can be broken, rendering the radar (and human observers) incapable of seeing the target.
 Additionally, radars of the era were subject to "
clutter" from stray returns from the ground and other objects, which meant a minimum angle existed above the horizon where they could detect a target. Bombers flying at low altitudes could remain under these angles simply by keeping their distance from the radar sites. This combination of effects made SAMs of the era ineffective against low-flying aircraft.
 The same effects also meant that low-flying aircraft were difficult to detect by higher-flying interceptors, since their radar systems could not readily pick out opposing aircraft against the clutter from ground reflections (lack of
The switch from high-altitude to low-altitude flight profiles severely affected the B-70, whose design was highly tuned to provide the desired high-altitude performance. Planners outlined a series of low-level profiles for the B-70, but higher
aerodynamic drag at low level limited the B-70 to subsonic speed while dramatically decreasing its range.
 The result would be an aircraft with somewhat higher subsonic speed than the B-52, but less range. Unsuited for the new low-altitude role, and because of a growing shift to the
intercontinental ballistic missile (ICBM) force, the B-70 bomber program was cancelled in 1961 by President
John F. Kennedy,
 and the two XB-70 prototypes were used in a supersonic research program.
Although never intended for the low-level role, the B-52's flexibility allowed it to outlast its intended successor as the nature of the air war environment changed. The B-52's huge fuel load allowed it to operate at lower altitudes for longer times, and the large airframe allowed the addition of improved
radar jamming and deception suites to deal with radars.
 During the
Vietnam War, the concept that all future wars would be nuclear was turned on its head, and the "big belly" modifications increased the B-52's total bomb load to 60,000 pounds (27,000 kg),
 turning it into a powerful tactical aircraft which could be used against ground troops along with strategic targets from high altitudes.
 The much smaller bomb bay of the B-70 would have made it much less useful in this role.
Design studies and delays
Although effective, the B-52 was not ideal for the low-level role. This led to a number of aircraft designs known as
penetrators, which were tuned specifically for long-range low-altitude flight. The first of these designs to see operation was the supersonic
F-111 fighter-bomber, which used variable-sweep wings for tactical missions.
 Similar aircraft also emerged for other users as well, notably the
BAC TSR-2, and later,
Panavia Tornado and
Sukhoi Su-24. A number of studies on a strategic-range counterpart followed.
The first post-B-70 strategic penetrator study was known as the Subsonic Low-Altitude Bomber (SLAB), which was completed in 1961. This produced a design that looked more like an airliner than a bomber, with a large swept wing,
T-tail, and large
 This was followed by the similar Extended Range Strike Aircraft (ERSA), which added a
variable-sweep wing, then in vogue in the aviation industry. ERSA envisioned a relatively small aircraft with a 10,000 pounds (4,500 kg) payload and a range of 8,750 nautical miles (16,200 kilometres), with 2,500 nmi (4,600 km) being flown at low altitudes. In August 1963, the similar Low-Altitude Manned Penetrator design was completed, which called for an aircraft with a 20,000 pounds (9,100 kg) bomb load and somewhat shorter range of 7,150 nmi (13,240 km).
These all culminated in the October 1963 Advanced Manned Precision Strike System (AMPSS), which led to industry studies at
General Dynamics, and
 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, similar to that of the existing Mach 2 class
Convair B-58 Hustler.
 Given the lengthy series of design studies, Rockwell engineers joked that the new name actually stood for "America's Most Studied Aircraft".
The arguments that led to the cancellation of the B-70 program had led some to question the need for a new strategic bomber of any sort. The USAF was adamant about retaining bombers as part of the
nuclear triad concept that included bombers, ICBMs, and
submarine-launched ballistic missiles (SLBMs) in a combined package that complicated any potential defense. They argued that the bomber was needed to attack hardened military targets and to provide a safe
counterforce option because the bombers could be quickly launched into safe loitering areas where they could not be attacked. However, the introduction of the SLBM made moot the mobility and survivability argument, and a newer generation of ICBMs, such as the
Minuteman III, had the accuracy and speed needed to attack point targets. During this time, ICBMs were seen as a less costly option based on their lower unit cost,
 but development costs were much higher.
Secretary of Defense
Robert McNamara preferred ICBMs over bombers for the Air Force portion of the deterrent force
 and felt a new expensive bomber was not needed.
 McNamara limited the AMSA program to studies and component development beginning in 1964.
Program studies continued;
Autonetics were awarded AMSA advanced avionics study contracts in 1968.
 McNamara remained opposed to the program in favor of upgrading the existing B-52 fleet and adding nearly 300
FB-111s for shorter range roles then being filled by the B-58.
 He again vetoed funding for AMSA aircraft development in 1968.
AN/APQ-140 radar for the B-1A
Richard Nixon reestablished the AMSA program after taking office, keeping with his administration's
flexible response strategy that required a
broad range of options short of general nuclear war.
 Nixon's Secretary of Defense,
Melvin Laird, reviewed the programs and decided to lower the numbers of FB-111s, since they lacked the desired 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. The Air Force issued a request for proposals in November 1969.
Proposals were submitted by Boeing, General Dynamics and North American Rockwell in January 1970.
 In June 1970, North American Rockwell's design was selected and was awarded a development contract.
 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.
 The company changed its name to
Rockwell International and named its aircraft division North American Aircraft Operations in 1973.
 A fourth prototype, built to production standards, was ordered in the fiscal year 1976 budget. Plans called for 240 B-1As to be built, with
initial operational capability set for 1979.
Rockwell's design featured a number of features common to 1960s U.S. designs. Among these was the use of a
crew escape capsule that ejected as a unit during emergencies, which was introduced to improve survivability in the case of an ejection at high speed. Additionally, the design featured large 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
Soviet Union's defenses would take place at
supersonic speed, 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 the "dash" portion of the flight to be relatively long.
In order to achieve the required Mach 2 performance at high altitudes, the exhaust nozzles and air
intake ramps were 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. The low altitude performance requirement was later lowered to Mach 0.85, reducing the amount of titanium and therefore cost.
 A pair of small
vanes mounted near the nose are part of an active vibration damping system that smooths out the otherwise bumpy low-altitude ride.
 The first three B-1As featured the escape capsule that ejected the cockpit with all four crew members inside. The fourth B-1A was equipped with a conventional
ejection seat for each crew member.
The B-1A mockup review occurred in late October 1971.
 The first B-1A prototype (Air Force serial no. 74-0158) flew on 23 December 1974. Three more B-1A prototypes followed.
 As the program continued the per-unit cost continued to rise in part because of high
inflation during that period. In 1970, the estimated unit cost was $40 million, and by 1975, this figure had climbed to $70 million.
New problems and cancellation
B-1A Prototype 4 showing its underside in 1981
B-1A nose section with ejection capsule denoted. Three of the four B-1As were fitted with escape capsules.
In 1976, Soviet pilot
Viktor Belenko defected to
Japan with his
 During debriefing he described a new "super-Foxbat" (almost certainly referring to the
MiG-31) that had
radar in order to attack cruise missiles. This would also make any low-level penetration aircraft "visible" and easy to attack.
 Given that the B-1's armament suite was similar to the B-52, and it now appeared no more likely to survive Soviet airspace than the B-52, the program was increasingly questioned.
 In particular, Senator
William Proxmire continually derided the B-1 in public, arguing it was an outlandishly expensive dinosaur. During the
1976 federal election campaign,
Jimmy Carter made it one of the Democratic Party's platforms, saying "The B-1 bomber is an example of a proposed system which should not be funded and would be wasteful of taxpayers' dollars."
When Carter took office in 1977 he ordered a review of the entire program. By this point the projected cost of the program had risen to over $100 million per aircraft, although this was lifetime cost over 20 years. He was informed of the relatively new work on
stealth aircraft that had started in 1975, and he decided that this was a better avenue of approach than the B-1.
Pentagon officials also stated that the
AGM-86 Air Launched Cruise Missile (ALCM) launched from the existing B-52 fleet would give the USAF equal capability of penetrating Soviet airspace. With a range of 1,500 miles (2,400 km), the ALCM could be launched well outside the range of any Soviet defenses and penetrate at low altitude like a bomber (with a much lower
radar cross-section due to smaller size), and in much greater numbers at a lower cost.
 A small number of B-52s could launch hundreds of ALCMs, saturating the defense. A program to improve the B-52 and develop and deploy the ALCM would cost perhaps 20% of the price to deploy the planned 244 B-1As.
On 30 June 1977, Carter announced that the B-1A would be canceled in favor of ICBMs, SLBMs, and a fleet of modernized B-52s armed with ALCMs.
 Carter called it "one of the most difficult decisions that I've made since I've been in office." No mention of the stealth work was made public with the program being
top secret, but today it is known that in early 1978 he authorized the Advanced Technology Bomber (ATB) project, which eventually led to the
Domestically, the reaction to the cancellation was split along partisan lines. The Department of Defense was surprised by the announcement; internal expectations were that the number of B-1s ordered would be reduced to around 150.
Robert Dornan (R-CA) claimed, "They're breaking out the vodka and caviar in Moscow."
 In contrast, it appears the Soviets were more concerned by large numbers of ALCMs representing a much greater threat than a smaller number of B-1s. Soviet news agency
TASS commented that "the implementation of these militaristic plans has seriously complicated efforts for the limitation of the strategic arms race."
 Western military leaders were generally happy with the decision. NATO commander
Alexander Haig described the ALCM as an "attractive alternative" to the B-1. French General Georges Buis stated "The B-1 is a formidable weapon, but not terribly useful. For the price of one bomber, you can have 200 cruise missiles."
Flight tests of the four B-1A prototypes for the B-1A program continued through April 1981. The program included 70 flights totaling 378 hours. A top speed of Mach 2.22 was reached by the second B-1A. Engine testing also continued during this time with the YF101 engines totaling almost 7,600 hours.
It was during this period that the Soviets started to assert themselves in several new theaters of action, in particular through
Cuban proxies during the
Angolan Civil War starting in 1975 and the
Soviet invasion of Afghanistan in 1979. U.S. strategy to this point had been focused on
Communism and preparation for war in Europe. The new Soviet actions revealed that the military lacked capability outside these narrow confines.
The U.S. Department of Defense responded by accelerating its
Rapid Deployment Forces concept but suffered from major problems with airlift and sealift capability.
 In order to slow an enemy invasion of other countries, air power was critical; however the key Iran-Afghanistan border was outside the range of the
U.S. Navy's carrier-based attack aircraft, leaving this role to the U.S. Air Force. Although the B-52 had the range to support on-demand global missions, its long runway requirements limited the forward basing possibilities.
During the 1980 presidential campaign,
Ronald Reagan campaigned heavily on the platform that Carter was weak on defense, citing the cancellation of the B-1 program as an example, a theme he continued using into the 1980s.
 During this time Carter's defense secretary,
Harold Brown, announced the stealth bomber project, apparently implying that this was the reason for the B-1 cancellation.
On taking office, Reagan was faced with the same decision as Carter before: whether to continue with the B-1 for the short term, or to wait for the development of the ATB, a much more advanced aircraft. Studies suggested that the existing B-52 fleet with
ALCM would remain a credible threat until 1985. It was predicted that 75% of the B-52 force would survive to attack its targets.
 After this, the introduction of the
SA-10 missile, the MiG-31 interceptor and the first Soviet
Airborne Early Warning and Control (AWACS) systems would make the B-52 increasingly vulnerable.
 During 1981, funds were allocated to a new study for a bomber for the 1990s time-frame which led to developing the Long-Range Combat Aircraft (LRCA) project. The LRCA evaluated the B-1, F-111, and ATB as possible solutions; an emphasis was placed on multi-role capabilities, as opposed to purely strategic operations.
In 1981, it was believed the B-1 could be in operation before the
ATB, covering the transitional period between the B-52's increasing vulnerability and the ATB's introduction. Reagan decided the best solution was to procure both the B-1 and ATB, and on 2 October 1981 he announced that 100 B-1s were to be ordered to fill the LRCA role.
In January 1982, the U.S. Air Force awarded two contracts to Rockwell worth a combined $2.2 billion for the development and production of 100 new B-1 bombers.
 Numerous changes were made to the design to make it better suited to the now expected missions, resulting in the new B-1B.
 These changes included a reduction in maximum speed,
 which allowed the variable-aspect
intake ramps to be replaced by simpler fixed geometry intake ramps in the newer design. This reduced the B-1B's radar signature or
radar cross-section; this reduction was seen as a good trade off for the speed decrease.
 High subsonic speeds at low altitude became a focus area for the revised design,
 and low-level speeds were increased from about Mach 0.85 to 0.92. The B-1B has a maximum speed of Mach 1.25 at higher altitudes.
The B-1B's maximum takeoff weight was increased to 477,000 pounds (216,000 kg) from the B-1A's 395,000 pounds (179,000 kg).
 The weight increase was to allow for takeoff with a full internal fuel load and for external weapons to be carried. Rockwell engineers were able to reinforce critical areas and lighten non-critical areas of the airframe, so the increase in
empty weight was minimal.
 To deal with the introduction of the
MiG-31 equipped with the new
Zaslon radar system, and other aircraft with
look-down capability (which reduced the B-1s low-flying advantage), the B-1B's
electronic warfare suite was significantly upgraded.
B-1B banking during a demonstration in 2004
Opposition to the plan was widespread within Congress. Critics pointed out that many of the original problems remained in both areas of performance and expense.
 In particular it seemed the B-52 fitted with electronics similar to the B-1B would be equally able to avoid interception, as the speed advantage of the B-1 was now minimal. It also appeared that the "interim" time frame served by the B-1B would be less than a decade, being rendered obsolete shortly after the introduction of a much more capable ATB design.
 The primary argument in favor of the B-1 was its large
conventional weapon payload, and that its takeoff performance allowed it to operate with a credible bomb load from a much wider variety of airfields. The USAF spread production subcontracts across many congressional districts, making the aircraft more popular on
B-1A #1 was disassembled and used for radar testing at the
Rome Air Development Center at the former
Griffiss Air Force Base,
 B-1As #2 and #4 were then modified to include B-1B systems. The first B-1B was completed and began flight testing in March 1983. The first production B-1B was rolled out on 4 September 1984 and first flew on 18 October 1984.
 The 100th and final B-1B was delivered on 2 May 1988;
 before the last B-1B was delivered, the USAF had determined that the aircraft was vulnerable to Soviet air defenses.