B-52 Stratofortress

The Boeing B-52 Stratofortress is a long-range, subsonic, jet-powered, strategic bomber operated by the United States Air Force (USAF) since 1955.

Beginning with the successful contract bid on 5 June 1946, the B-52 went through several design steps; from a straight wing aircraft powered by six turboprop engines to the final prototype YB-52, with eight turbojet engines. The aircraft made its first flight on 15 April 1952 with "Tex" Johnston as pilot.

Built to carry nuclear weapons for Cold War-era deterrence missions, the B-52 Stratofortress replaced the Convair B-36. Although a veteran of a number of wars, the Stratofortress has dropped only conventional munitions in actual combat. The B-52 carries up to 70,000 pounds (32,000 kg) of weapons.

The USAF has had B-52s in active service since 1955, initially with the Strategic Air Command (SAC), with all aircraft later absorbed into the Air Combat Command (ACC) following SAC's disestablishment in 1992. Superior performance at high subsonic speeds and relatively low operating costs have kept the B-52 in service despite proposals to replace it with the Mach 3 XB-70 Valkyrie, supersonic B-1B Lancer and stealthy B-2 Spirit. In January 2005, the B-52 became the second aircraft, after the English Electric Canberra, to mark 50 years of continuous service with its original primary operator. There are six aircraft altogether that have made this list as of 2009; the other four being the Tupolev Tu-95, the C-130 Hercules, the KC-135 Stratotanker, and the Lockheed U-2.

Development
Background
On 23 November 1945, Air Materiel Command (AMC) issued desired performance characteristics for a new strategic bomber "capable of carrying out the strategic mission without dependence upon advanced and intermediate bases controlled by other countries". The aircraft was to have a crew of five plus turret gunners, and a six-man relief crew. It had to cruise at 300 mph (240 kn, 480 km/h) at 34,000 feet (10,400 m) with a combat radius of 5,000 statute miles (4,300 nmi, 8,000 km). The armament was to consist of an unspecified number of 20 mm cannon and 10,000 pounds (4,500 kg) of bombs. On 13 February 1946, the Air Force issued bid invitations for these specifications, with Boeing, Consolidated Aircraft, and Glenn L. Martin Company submitting proposals.

On 5 June 1946, Boeing's Model 462, a straight-wing aircraft powered by six Wright T35 turboprops with a gross weight of 360,000 pounds (160,000 kg) and combat radius of 3,110 statute miles (2,700 nmi, 5,010 km), was declared the winner. On 28 June 1946, Boeing was issued a letter of contract for US$1.7 million (1946 dollars) to build a full-scale mock-up of the new XB-52 and do preliminary engineering and testing. However, by October 1946, the Air Force began to express concern about the sheer size of the new aircraft and its inability to meet the specified design requirements. In response, Boeing produced Model 464, a smaller four-engine version with a 230,000 pound (105,000 kg) gross weight, which was briefly deemed acceptable.

Then, in November 1946, the Deputy Chief of Air Staff for Research and Development, General Curtis LeMay, expressed the desire for a cruise speed of 400 miles per hour (345 kn, 645 km/h), to which Boeing responded with a 300,000 pound (140,000 kg) aircraft. In December 1946, Boeing was asked to change their design to a four-engine bomber with a top speed of 400 miles per hour, range of 12,000 statute miles (10,000 nmi, 19,000 km), and the ability to carry a nuclear weapon. The aircraft could weigh up to 480,000 pounds (220,000 kg). Boeing responded with two models powered by the T-35 turboprops. The Model 464-16 was a "nuclear-only" bomber with a 10,000 pound payload, while the Model 464-17 was a general purpose bomber with a 90,000 pound (40,000 kg) payload. Due to the cost associated with purchasing two specialized aircraft, the Air Force selected Model 464-17 with the understanding that it could be adapted for nuclear strikes.

In June 1947, the military requirements were updated and the Model 464-17 met all of them except for the range. It was becoming obvious to the Air Force that, even with the updated performance, the XB-52 would be obsolete by the time it entered production and would offer little improvement over the Convair B-36. As a result, the entire project was put on hold for six months. During this time, Boeing continued to perfect the design which resulted in the Model 464-29 with a top speed of 455 miles per hour (395 kn, 730 km/h) and a 5,000-mile range. In September 1947, the Heavy Bombardment Committee was convened to ascertain performance requirements for a nuclear bomber. Formalized on 8 December 1947, these called for a top speed of 500 miles per hour (440 kn, 800 km/h) and an 8,000 statute mile (7,000 nmi, 13,000 km) range, far beyond the capabilities of 464-29.

The outright cancellation of the Boeing contract on 11 December 1947 was staved off by a plea from its president William McPherson Allen, and in January 1948 Boeing was instructed to thoroughly explore recent technological innovations, including aerial refueling and the flying wing. Noting stability and control problems Northrop was experiencing with their YB-35 and YB-49 flying wing bombers, Boeing insisted on a conventional aircraft, and in April 1948 presented a US$30 million (1948 dollars) proposal for design, construction, and testing of two Model 464-35 prototypes. Further revisions of specifications during 1948 resulted in an aircraft with a top speed of 513 miles per hour (445 kn, 825 km/h) at 35,000 feet (10,700 m), a range of 6,909 statute miles (6,005 nmi, 11,125 km), and a 280,000 pounds (125,000 kg) gross weight which included 10,000 pounds of bombs and 19,875 US gallons (75,225 L) of fuel.

Production

In May 1948 AMC asked Boeing to incorporate the previously discarded, but now more fuel-efficient, jet engine into the design. This resulted in Boeing developing yet another revision — in July 1948, Model 464-40 substituted Westinghouse J40 turbojets for the turboprops. Nevertheless, on 21 October 1948, Boeing was told to create an entirely new aircraft using Pratt & Whitney J57 turbojets.

On 25 October, Boeing engineers produced a proposal and a hand-carved model of 464-49. The new design built upon the basic layout of the B-47 Stratojet with 35° swept wings, eight engines paired in four underwing pods, and bicycle landing gear with wingtip outrigger wheels. A notable feature of the landing gear was the ability to pivot the main landing gear up to 20° from the aircraft centerline to increase safety during crosswind landings. The aircraft was projected to exceed all design specifications. Although the full-size mock-up inspection in April 1949 was generally favorable, range again became a concern since the J40s and the early model J57s had excessive fuel consumption. Despite talk of another revision of specifications or even a full design competition among aircraft manufacturers, General LeMay, now in charge of Strategic Air Command, insisted that performance should not be compromised due to delays in engine development. In a final attempt to increase the range, Boeing created the larger 464-67, stating that once in production, the range could be further increased in subsequent modifications. Following several direct interventions by LeMay, on 14 February 1951 Boeing was awarded a production contract for 13 B-52As and 17 detachable reconnaissance pods. The last major design change, also at the insistence of General LeMay, was a switch from the B-47 style tandem seating to a more conventional side-by-side cockpit which increased the effectiveness of the copilot and reduced crew fatigue. Both XB-52 prototypes featured the original tandem seating arrangement with a framed bubble-type canopy. The YB-52 (actually, the second XB-52 with more operational equipment) first flew on 15 April 1952, a 2 hour 21 minute flight from Renton Field in Renton, Washington to Larson AFB with Boeing test pilot Alvin M. Johnston and Air Force Lieutenant Colonel Guy M. Townsend. The XB-52 followed on 2 October 1952. The thorough development, including 670 days in the wind tunnel and 130 days of aerodynamic and aeroelastic testing, paid off with smooth flight testing. Encouraged, the Air Force increased its order to 282 B-52s.

Only three of the 13 B-52As ordered were built. All were returned to Boeing, and used in their test program. On 9 June 1952 the February 1951 contract was updated to order the aircraft under new specifications. The final ten—the first aircraft to enter active service—were completed as B-52Bs. At the roll out ceremony on 18 March 1954, Air Force Chief of Staff, General Twining said:

Design
Upgrades and modifications
In November 1959, SAC initiated the Big Four modification program (also known as Modification 1000) for all operational B-52s except early B models. The program was completed by 1963. The four modifications were:

Ability to perform all-weather, low-altitude (below 500 feet (150 m)) interdiction as a response to advancements in Soviet Union's missile defenses. The low-altitude flights were estimated to accelerate structural fatigue by at least a factor of eight, requiring costly repairs to extend service life.

Ability to launch AGM-28 Hound Dog standoff nuclear missiles
Ability to launch ADM-20 Quail decoys
An advanced electronic countermeasures (ECM) suite
The ability to carry up to 20 AGM-69 SRAM nuclear missiles was added to G and H models starting in 1971. Fuel leaks due to deteriorating Marman clamps continued to plague all variants of the B-52. To this end, the aircraft were subjected to Blue Band (1957), Hard Shell (1958), and finally QuickClip (1958) programs. The latter fitted safety straps which prevented catastrophic loss of fuel in case of clamp failure.

Ongoing problems with advanced avionics were addressed in the Jolly Well program, completed in 1964, which improved components of the AN/ASQ-38 bombing navigational computer and the terrain computer. The MADREC (Malfunction Detection and Recording) upgrade fitted to most aircraft by 1965 could detect failures in avionics and weapons computer systems, and was essential in monitoring the Hound Dog missiles. The electronic countermeasures capability of the B-52 was expanded with Rivet Rambler (1971) and Rivet Ace (1973).

In order to improve the ability to operate safely at low level during both day and night, the AN/ASQ-151 Electro-Optical Viewing System (EVS), consisting of a Low Light Level Television (LLLTV) and a Forward Looking Infra-Red (FLIR) system mounted in blisters under the noses of B-52Gs and Hs between 1972 and 1976. In order to further improve the B-52s offensive ability, it was decided to fit Air Launched Cruise Missiles (ALCMs). After testing of both the Air-Force backed Boeing AGM-86 and the Navy backed General Dynamics AGM-109 Tomahawk, the AGM-86B was selected for operation by the B-52 (and ultimately by the B-1 Lancer). A total of 194 B-52Gs and Hs were modified to carry AGM-86s, carrying 12 missiles on underwing pylons, with 82 B-52Hs further modified to carry another eight missiles on a rotary launcher fitted in the aircraft's bomb-bay. In order to conform with the requirements of the SALT II Treaty for cruise missile capable aircraft to be readily identified by reconnaissance satellites, the cruise missile armed B-52Gs were modified with a distinctive wing root fairing. As all B-52Hs were assumed to be modified, no visual modification of these aircraft was required. In 1990, the stealthy AGM-129 ACM cruise missile entered service. Although originally intended to replace the AGM-86 its high cost and the end of the Cold War stopped production after only 450 had been made. Unlike the AGM-86, no conventional (i.e. non-nuclear) armed version was built.

Structural fatigue, exacerbated by the change to low-altitude missions, was first dealt with in the early 1960s by the three-phase High Stress program which enrolled aircraft at 2,000 flying hours. This was followed by a 2,000-hour service life extension to select airframes in 1966-1968, and the extensive Pacer Plank reskinning completed in 1977. The wet wing introduced on G and H models was even more susceptible to fatigue due to experiencing 60% more stress during flight than the old wing. The wings were modified by 1964 under ECP 1050. This was followed by a fuselage skin and longeron replacement (ECP 1185) in 1966, and B-52 Stability Augmentation and Flight Control program (ECP 1195) in 1967.

Boeing has suggested re-engining the B-52H fleet with the Rolls-Royce RB211 534E-4. This would involve replacing the eight Pratt & Whitney TF33s (total thrust 8 × 17,000 lb) with four RB211s (total thrust 4 × 37,400lb). The RR engines will increase the range and payload of the fleet and reduce fuel consumption. However, the cost of the project would be significant. Procurement would cost approximately US$2.56 billion (US$36 million × 71 aircraft). A Government Accountability Office study of the proposal concluded that Boeing's estimated savings of US$4.7 billion would not be realized. They found that it would cost the Air Force US$1.3 billion over keeping the existing engines. This was subsequently disputed in a Defense Sciences Board report in 2003 and revised in 2004 that identified numerous errors in the prior evaluation of the Boeing proposal, and urged the Air Force to re-engine the aircraft without delay. Further, the DSB report stated the program would save substantial funds, reduce greenhouse gas emissions, and increase aircraft range and endurance, duplicating the results of a Congressionally funded US$3M program office study conducted in 2003. However, the re-engining has been approved as of 2009.

In 2007 the LITENING targeting pod was fitted and commissioned increasing the combat effectiveness of the aircraft during day, night and under-the-weather conditions in the attack of ground targets with a variety of standoff weapons under the guidance of LASERs and the help of high resolution forward-looking infrared sensor (FLIR) for visual display in the infrared portion of the electromagnetic spectrum and charged coupled device (CCD-TV) camera used to obtain target imagery in the visible portion, this technology could also be used in real-time transmission to ground communications networks and government agencies to gather battlefield intelligence, assess battlefield damage, assess terrorist activities and counter drug activity, further advancing the B-52H's capabilities and uses.

Fuel research platform
In September 2006, the B-52 became one of the first US military aircraft to fly using 'alternative' fuel. Syntroleum Corporation, a leader in Fischer-Tropsch process (FT) technology, announced that its Ultra-Clean jet fuel had been successfully tested in a B-52. It took off from Edwards Air Force Base with a 50/50 blend of FT and traditional JP-8 jet fuel which was burned in two of the eight engines on the aircraft. This marked the first time that FT jet fuel was tested in a military flight demo, and is the first of several planned test flights.

On 15 December 2006, tail number 61-0034, Wise Guy took off from Edwards with the synthetic fuel blend powering all eight engines, the first time an Air Force aircraft was completely powered by the mixture. The test flight was captained by Major General Curtis Bedke, commander of the Edwards Flight Test Center, the first time in 36 years that the installation's commander performed a first flight in a flight test program. The flight lasted seven hours, reached an altitude of 48,000 feet, and was considered a success.

On 8 August 2007, Air Force Secretary Michael Wynne certified the B-52H as fully approved to use the FT blend, marking the formal conclusion of the test program.

This program is part of the Department of Defense Assured Fuel Initiative, an effort to develop secure domestic sources for the military energy needs. The Pentagon hopes to reduce its use of crude oil from foreign producers and obtain about half of its aviation fuel from alternative sources by 2016. With the B-52 now approved to use the FT blend, the USAF will use the test protocols developed during the program to certify the C-17 Globemaster III and then the B-1B to use the fuel (the first B-1 test flight took place in March, 2008). The Air Force intends to test and certify every airframe in its inventory to use the fuel by 2011.

B-2 Spirit

The Northrop Grumman B-2 Spirit (also known as the "Stealth Bomber") is a multirole heavy bomber with "low observable" stealth technology capable of penetrating dense anti-aircraft defenses to deploy both conventional and nuclear weapons. Because of its considerable capital and operations costs, the project was controversial in Congress and among Pentagon brass during its development and placement into service. During the late 1980s and early 1990s, the United States scaled back initial plans to purchase 132 of the bombers. By the mid 1990s, Congress made appropriations to purchase a total fleet of just 21 of the bombers.

The cost of each air vehicle averaged US$737 million per plane in 1997 dollars. Total procurement costs averaged US$929 million per plane, which includes spare parts, equipment, retrofitting, and software support. The total program cost, which includes development, engineering and testing, averaged US$2.1 billion per aircraft in 1997 dollars.

Twenty B-2s are operated by the United States Air Force. Though originally designed in the 1980s for Cold War operations scenarios, B-2s have been used in combat to drop bombs on Kosovo in the late 1990s, and see continued use during the ongoing wars in Iraq and Afghanistan. One aircraft was lost when it crashed on takeoff in 2008.

The crew of two aboard the bomber can drop up to eighty 500 lb (230 kg) class JDAM "smart" bombs, or sixteen 2,400 lb (1,100 kg) B83 nuclear bombs in a single pass through extremely dense anti-aircraft defenses. It has been the subject of espionage and counter-espionage activity. The bomber has been a prominent public spectacle at air shows since the 1990s.

Development
ATB project
The B-2 Spirit originated from the Advanced Technology Bomber (ATB) black project that began in 1979. The Cold War was well underway, and on the campaign trail in 1979 and 1980, candidate Ronald Reagan promised a restoration of American military strength. On 22 August 1980, the incumbent Carter administration publicly disclosed that the Department of Defense was working to develop stealth aircraft including the ATB.

After the evaluations of the companies' proposals, the ATB competition was reduced to the Northrop/Boeing and Lockheed/Rockwell teams with each receiving a study contract for further work. The Northrop design was larger while the Lockheed design was smaller and included a small tail. The black project was funded under the code name "Aurora". The Northrop/Boeing team's ATB design was selected over the Lockheed/Rockwell design on October 20, 1981.

The Northrop design received the designation B-2 and the name "Spirit". The bomber's design was changed in the mid-1980s when the mission profile was changed from high-altitude to low-altitude, terrain-following. The redesign delayed the B-2's first flight by two years and added about US$1 billion to the program's cost. An estimated US$23 billion was secretly spent for research and development on the B-2 by 1989. At the program's peak, approximately 13,000 people were employed at a dedicated plant in Pico Rivera, California for the plane's engineering and portions of its manufacturing.

The B-2 was first publicly displayed on November 22, 1988, at Air Force Plant 42, Palmdale, California, where it was assembled. Its first public flight was on July 17, 1989 from Palmdale.

Procurement
A procurement of 132 aircraft was planned in the mid-1980s, but was later reduced to 75. By the early 1990s, the Soviet Union had disintegrated, which effectively rendered void the Spirit's primary Cold War mission. In light of budgetary pressures and congressional opposition, in his 1992 State of the Union Address, President George H.W. Bush announced B-2 production would be limited to a total of 20 aircraft. In 1996, however, the Clinton administration, though originally committed to ending production of the bombers once the 20th aircraft was completed, authorized the conversion of a 21st bomber, a prototype test model, to Block 30 full operational status at a cost of nearly $500 million.

The bomber's high costs reflected the innovation of a paperless computer aided design (CAD) system, and a computerized manufacturing control system. The costs also reflect the inefficiencies of separating design teams into different parts of the country for both design intelligence compartmentalization as a counter-espionage measure, and by parceling out the supply chain with the requisite lucrative contracts to congressional districts as a political reward.
Northrop made a proposal to the USAF in 1995 to build 20 additional aircraft with a flyaway cost of $566M each.

Espionage
In 1984 a Northrop employee, Thomas Cavanaugh, was arrested for trying to sell classified information to the Soviet Union, which apparently was smuggled out of the Pico Rivera, California factory. Cavanaugh was eventually sentenced to life in prison and released under parole in 2001.

Noshir Gowadia, a design engineer who worked on the B-2's propulsion system, was arrested in October 2005 for selling B-2 related classified information to foreign countries. His trial was initially scheduled for 12 February 2008, but he received a continuance.

Program costs
The program was the subject of public controversy for its costs to American taxpayers. In 1996 the General Accounting Office disclosed that the B-2 bomber "will be, by far, the most costly bombers to operate on a per aircraft basis" costing over three times as much as the B-1B (US$9.6 million annually) and over four times as much as the B-52H ($US6.8 million annually). In September 1997, each hour of B-2 flight necessitated 119 hours of maintenance in turn. Comparable maintenance needs for the B-52 and the B-1B are 53 and 60 hours respectively for each hour of flight. A key reason for this cost are the air-conditioned hangars large enough for the bomber's 172 ft (52.4 m) wingspan, which are needed to maintain the aircraft's stealthy properties, especially its "low-observable" stealthy skins. These maintenance requirements raise serious questions about the ability to deploy the B-2 overseas.

The total "military construction" cost related to the program was projected to be US$553.6 million in 1997 dollars. The cost to procure each B-2 "air vehicle" was US$737 million in 1997 dollars based only on air vehicle cost of US$15.48 billion. The procurement cost per plane as detailed in General Accounting Office (GAO) reports, which include spare parts and software support, was $929 million per plane in 1997 dollars.

The total program cost projected through 2004 was US$44.75 billion in 1997 dollars. This includes development, procurement, facilities, construction, and spare parts. The total program cost averaged US$2.13 billion per plane.

Opposition
In its consideration of the fiscal year 1990 defense budget, the House Armed Services Committee trimmed $800 million from the B-2 research and development budget, while at the same time staving off a motion to kill the bomber. The opposition was bipartisan, with Congressman Ron Dellums (D-CA), John Kasich (R-OH), and John G. Rowland (R-CT) authorizing the motion to kill the bomber; the growing cost of the B-2 appeared to be the factor driving the opposition. At the peak production period specified in 1989, the schedule called for spending US$7 billion to $8 billion per year in 1989 dollars, something Committee Chair Les Aspin (D-WI) said "won't fly financially."

In time, a number of prominent members of Congress began to oppose the program's expansion, to include former Democratic presidential nominee John Kerry who cast votes against the B-2 Stealth Bomber in 1989, 1991 and 1992 while a United States Senator representing Massachusetts. By 1992, Republican President George H.W. Bush called for the cancellation of the B-2 and promised to cut military spending by 30% in the wake of the collapse of the Soviet Union.

In May 1995, on the basis of its 1995 Heavy Bomber Force Study, the DOD determined that additional B-2 procurements would exacerbate efforts to develop and implement long term recapitalization plans for the USAF bomber force.

In October 1995, former Chief of Staff of the United States Air Force, General Mike Ryan, and Former Chairman of the Joint Chiefs of Staff, General John Shalikashvili, strongly recommended against Congressional action to fund the purchase any additional B-2s, arguing that to do so would require unacceptable cuts in existing conventional and nuclear-capable aircraft to pay for the new bombers, and because the military had much higher priorities on which to spend its limited procurement dollars.

Some B-2 advocates argued that procuring twenty additional B-2s would save money because B-2s would be able to deeply penetrate anti-aircraft defenses and use low-cost, short-range attack weapons rather than expensive standoff weapons. However, in 1995, the Congressional Budget Office (CBO), and its Director of National Security Analysis, found that additional B-2s would reduce the cost of weapons expended by the bomber force by less than US$2 billion in 1995 dollars during the first two weeks of a conflict, which is when the Air Force envisions bombers would make their greatest contribution. This is a small fraction of the US$26.8 billion (in 1995 dollars) life cycle cost that the CBO projected an additional twenty B-2s would cost.

In 1997, as Ranking Member of the House Armed Services Committee and National Security Committee, Congressman Ron Dellums, a long-time opponent of the bomber, cited five independent studies and offered an amendment to that year's defense authorization bill to cap production of the bombers with the existing 21 aircraft. The amendment was narrowly defeated. Nonetheless, Congress has never approved funding for the purchase of any additional B-2 bombers to date.

Radar modernization
On 29 December 2008, Air Force officials awarded a production contract to Northrop Grumman to modernize the B-2 fleet's radar. The contract provides advanced state-of-the-art radar components, with the aim of sustained operational viability of the B-2 fleet into the future. The contract has a target value of approximately US$468 million. The award follows successful flight testing with the upgraded equipment. A modification to the radar was needed since the U.S. Department of Commerce required the B-2 to use a different radar frequency.

Design
As with the B-52 Stratofortress and B-1 Lancer, the B-2 provides the versatility inherent in manned bombers. Like other bombers, its assigned targets can be canceled or changed while in flight, the particular weapon assigned to a target can be changed, and the timing of attack, or the route to the target can be changed while in flight. In addition, its low-observable, or "stealth", characteristics give it the ability to penetrate an enemy's most sophisticated anti-aircraft defenses to attack its most heavily defended targets.

The prime contractor, responsible for overall system design, integration and support, is Northrop Grumman. Boeing, Raytheon (formerly Hughes Aircraft), G.E. and Vought Aircraft Industries, are subcontractors.

The blending of low-observable technologies with high aerodynamic efficiency and large payload gives the B-2 significant advantages over previous bombers. The U.S. Air Force purports the aircraft has "high aerodynamic efficiency" and states its range is approximately 6,000 nautical miles (6,905 mi (11,113 km). Also, its low-observation ability provides the B-2 greater freedom of action at high altitudes, thus increasing its range and providing a better field of view for the aircraft's sensors. It combines GPS Aided Targeting System (GATS) with GPS-aided bombs such as Joint Direct Attack Munition (JDAM). This uses its passive electronically scanned array APQ-181 radar to correct GPS errors of targets and gain much better than laser-guided weapon accuracy when "dumb" gravity bombs are equipped with a GPS-aided "smart" guidance tail kit. It can bomb 16 targets in a single pass when equipped with 1,000 or 2,000-pound (450 kg or 900 kg) bombs, or as many as 80 when carrying 500 lb (230 kg) bombs.

The B-2's stealth comes from a combination of reduced acoustic, infrared, visual and radar signatures, making it difficult for opposition defenses to detect, track and engage the aircraft. Many specific aspects of the low-observability process remain classified.

The B-2's low observability originates from stealth technology exploited for the F-117. Russian-born physicist and mathematician Pyotr Ufimtsev, whose theoretical work made the F-117 and B-2 possible, was hired by Northrop at one time. Additionally, the B-2's composite materials, special coatings and flying wing design, which reduces the number of leading edges contribute to its stealth characteristics. Each B-2 requires a climate-controlled hangar large enough for its 172-foot (52 m) wingspan to protect the operational integrity of its sophisticated radar absorbent material and coatings. The engines are buried within the wing to conceal the induction fans and hide their exhaust.

The B-2 has a crew of two: a pilot in the left seat, and mission commander in the right. The B-2 has provisions for a third crew member if needed. For comparison, the B-1B has a crew of four and the B-52 has a crew of five. B-2 crews have been used to pioneer sleep cycle research to improve crew performance on long sorties. The B-2 is highly automated, and, unlike two-seat fighters, one crew member can sleep, use a toilet or prepare a hot meal while the other monitors the aircraft.

In 1990, the Department of Defense accused Northrop of using faulty components in the flight control system. More recent issues with the bomber have included cracks in the tail. Efforts have also been made to reduce the probability of bird ingestion, which could damage engine fan blades.
In 2008, Congress funded upgrades to the B-2s weapon control systems.

Operational history
The first operational aircraft, christened Spirit of Missouri, was delivered to Whiteman A.F.B., Missouri, where the fleet is based, on 17 December 1993.[39] The B-2 reached initial operational capability on 1 January 1997.[40] Depot maintenance for the B-2 is accomplished by U.S. Air Force contractor support and managed at Oklahoma City Air Logistics Center at Tinker Air Force Base. Originally designed to deliver nuclear weapons, modern usage has shifted towards a flexible role with conventional and nuclear capability.

Into combat
The B-2 has seen service in three campaigns. Its combat debut was during the Kosovo War in 1999. It was responsible for destroying 33 percent of selected Serbian bombing targets in the first eight weeks of U.S. involvement in the War. During this war, B-2s flew non-stop to Kosovo from their home base in Missouri and back. The B-2 was the first aircraft to deploy GPS satellite guided JDAM "Smart Bombs" in combat use in Kosovo.

The B-2 has been used to drop bombs on Afghanistan in support of the ongoing War in Afghanistan. With the support of aerial refueling, the B-2 flew one of its longest missions to date from Whiteman Air Force Base, Missouri to Afghanistan and back.

During the ongoing War in Iraq, B-2s have operated from Diego Garcia and an undisclosed "forward operating location". Other sorties in Iraq have launched from Whiteman AFB. This resulted in missions lasting over 30 hours and one mission of over 50 hours. The designated "forward operating locations" have been previously designated as Guam and RAF Fairford, where new climate controlled hangers have been constructed. B-2s have been used during 22 sorties from Diego Garcia as well as 27 sorties from Whiteman AFB, and have released more than 1.5 million pounds of munitions, to include 583 JDAM "Smart Bombs" in 2003.

The B-2's combat use preceded a U.S. Air Force declaration of "full operational capability" in December 2003. The Pentagon's Operational Test and Evaluation 2003 Annual Report noted that the B-2's serviceability for Fiscal Year 2003 was still inadequate, mainly due to the maintainability of the B-2's low observable coatings. The evaluation also noted that the Defensive Avionics suite also had shortcomings with pop-up threats.

All B-2s, nuclear-capable B-52s, and nuclear intercontinental ballistic missiles, have shifted to the new nuclear-focused Global Strike Command scheduled to be set up by September 2009.

B-1 Lancer

The B-1 Lancer is a strategic bomber used by the United States Air Force. First envisioned in the 1960s as a supersonic bomber with sufficient range and payload to replace the B-52 Stratofortress, it developed primarily into a low-level penetrator with long-range and capable of supersonic speed. The design was canceled and reinstated multiple times over its lengthy development history, as the theory of strategic balance changed from flexible response to mutually assured destruction and back again. It eventually entered service more than 20 years after first being studied.

The B-1B production version has been in service with the United States Air Force (USAF) since 1986. The Lancer serves as the supersonic component of the USAF's long-range bomber force, along with the subsonic B-52 and B-2 Spirit. The bomber is commonly called the "Bone" (originally from "B-One"). With the retirement of the EF-111 Raven in 1998 and the F-14 Tomcat in 2006, the B-1B is the U.S. military's only variable-sweep wing aircraft.

Development
The B-1 was conceived as the Advanced Manned Strategic Aircraft (AMSA) program around 1965. AMSA was the last in a series of 1960s programs that looked at replacing the B-52 with a long-range multi-role supersonic aircraft that could drop bombs and launch nuclear missiles.

The Valkyrie and changing tactics
In December 1957, U.S. Air Force selected North American Aviation's proposal to replace the B-52 Stratofortress. This would lead to the B-70 Valkyrie. The Valkyrie was a six-engine bomber that could fly very high at Mach 3 to avoid interceptor aircraft, the only effective anti-bomber weapon in the 1950s. At the time, Soviet interceptors were unable to intercept the high-flying Lockheed U-2; the Valkyrie was to fly at similar altitudes and much higher speeds. But by the late 1950s, anti-aircraft surface-to-air missiles (SAMs) could threaten high-altitude aircraft, as demonstrated by the downing of Gary Powers' U-2 in 1960.

Recognizing this, the USAF Strategic Air Command had begun moving to low-level penetration before the U-2 downing. This greatly reduces radar detection distances while at that time SAMs were ineffective and interceptors less effective against low-flying aircraft. Also the flight path to a target could be routed around known anti-aircraft sites, and the landscape could be used to the bomber's advantage to stay out of the radar's line-of-sight operation. Aircraft speed became much less important. The targets themselves often had defenses located nearby to prevent this sort of approach all the way in, but stand-off weapons such as the AGM-69 SRAM provided an attack capability from outside the defensive missile's range. Low-altitude flight also made the bombers very difficult to detect from aircraft at higher altitudes, including interceptors, as radar systems of that generation could not "look down" due to the clutter that resulted from ground reflections.

Operations at low levels would limit the B-70 to subsonic speed, while dramatically decreasing its range due to much higher fuel requirements. The result would be an aircraft with similar speed but much less range than the B-52 it would have replaced. The Mach 2 B-58 was similarly limited to subsonic speeds at low altitudes. Unsuited for this new role, the viability of the B-70 as a bomber was questioned. Citing high cost, a growing ICBM force, and poor survivability against missiles, the operational bomber fleet was canceled in 1961 by President John F. Kennedy, and the program was changed to a supersonic research program with two XB-70 prototype aircraft.

B-1A program
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. 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. 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.

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.

In 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.