Reviving big bombers for the USAF

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Date Posted: 05-May-2004

INTERNATIONAL DEFENSE REVIEW – JUNE 01, 2004

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Back to the bomber
Bill Sweetman

As recently as three years ago, the big bomber was reckoned to be a dinosaur. Bill Sweetman outlines the progress of plans in the US to revive the development of heavyweight attack aircraft

Plans for a new US Air Force (USAF) bomber are slowly gathering speed. By the late 1990s, the service seemed dedicated to paying lip-service to such a concept: the USAF bomber roadmap, published in March 1999, called for no serious investment in a new bomber before 2025-30. Due to the small numbers of B-2s and supportability issues with B-1Bs, the bomber force in the 2030s would be increasingly dominated by septuagenarian B-52Hs. It was hard to argue with a dissenting report, commissioned by Congress and published in 1998, which concluded that “under current plans the bomber has no future”.

That was before the terrorist attacks of 11 September 2001 and the conflicts in Afghanistan and Iraq. Denied access to bases nearest to the theaters of operations, through political pressure and terrorist threats, the USAF is realizing that the weapon in which it has invested more than 90% of its aircraft procurement funds, the single-seat tactical fighter, can be rendered much less effective by closing a few bases, which can be achieved as effectively by politics and diplomacy as by military force. Fighters in the Afghan and Iraqi campaign flew long missions with the aid of in-flight refueling, but the process was complex, extremely demanding for pilots and inefficient.

Bombers, however, proved well able to handle great distances and long missions. Two examples stood out: the use of B-52s, armed with Joint Direct Attack Munition (JDAM) guided bombs and bombing on Global Positioning System (GPS) cues provided by ground observers to attack Taliban positions; and the mission in which an orbiting B-1B received instructions to hit a building in Baghdad and did so, with four JDAMs, within 12 minutes of receiving co-ordinates.

Early in April, USAF Vice Chief of Staff General Michael Moseley delivered the firmest pro-bomber statement to be heard from such a senior leader in years. “Bombers cost-effectively deliver a robust, combat-proven, man-in-the-loop responsive capability, reaching any point on earth less than 24 hours after launch from a CONUS [continental US] base and faster from overseas bases,” Moseley told Congress. “Additionally, bombers carry the widest array of weapons in the air force inventory, with unparalleled flexibility to adapt to future weapons that enter the inventory.”

Moseley went on to announce that the USAF was starting an effort to field a new long-range strike (LRS) system by 2025-30. That means a full-rate production decision in 2020-25 and a start to systems development and demonstration in 2012-15, and that in turn means that real money must be available for science and technology investment within the current five-year budget plan. After a number of studies by the USAF and independent groups such as the Institute for Defense Analysis, an LRS office was established in February 2004, led by Air Force Materiel Command (AFMC).

What the LRS system will actually look like remains undefined. Moseley did, however, eliminate two candidates – hypersonic and high-supersonic systems – on the grounds that they cannot be developed in time. Another reason emerges from a USAF study that was due to be presented on 12 September 2001 – the date perhaps explains why it received little attention at the time – that focused on the value and cost of flying at different speeds. Even for a 13,000km distance from base to target, a Mach 2 (M2) cruiser reached the target eight hours faster than a subsonic aircraft; an M4 aircraft saved only another three hours. The faster an aircraft cruises, the longer it takes to accelerate and decelerate on take-off, on landing or for refueling. The study also made the reasonable assumption that an advanced M4 aircraft cannot be turned round as quickly as a low supersonic design.

Moseley’s civilian boss, Air Force Secretary James Roche, gave more perspective on the service’s LRS thinking in remarks to the Defense Advanced Research Projects Agency’s DARPATech conference in March. “We’ve done all we can to put the burden on sensors and weapons and keep the old platforms,” Roche said. He went on to outline the idea of a “regional bomber”. Roche explained that the new aircraft would be very stealthy and – like the F/A-22 but unlike the F-117 and B-2 – would operate by day and at night. “That means,” he said, “that it either fights back or is fast enough to scoot away.” Because of the requirements for stealth plus either speed or air combat capability, “the idea of a great big intercontinental bomber doesn’t come up”.

Roche added that the regional bomber “will be a bridge to a world that has very different long-range strike systems”; Moseley, in his testimony to Congress, remarked that the USAF would continue to fund hypersonic technology to provide a global strike capability by around 2050.

The idea of a supersonic-cruise bomber is unfamiliar only to those who have forgotten the North American XB-70 Valkyrie, designed as a replacement for the B-52. Canceled in the 1960s by the then Defense Secretary Robert McNamara, the 243t XB-70 was designed to carry a 22t bomb load for a 14,000km unrefueled range at a cruising speed of around M3. The XB-70 never attained its design performance: the first of two prototypes (built as pure research aircraft) was plagued by problems with its stainless-steel honeycomb structure and 275-bar hydraulic system, and the second was lost in an accident. Arguably, though, if it was possible to build the XB-70 40 years ago it should be possible to build a smaller, shorter-range and slower LRS 10 years in the future.

Arsenal aircraft

Congress has been pushing the idea of a new bomber for some time. A proposal early in 2001 to resurrect the B-2 as a conventional bomber gained some adherents despite underwhelming support from the USAF itself. The winner-take-all approach to the Joint Strike Fighter has encouraged politicians from the so-called ‘Boeing states’ to support a bomber program as a way of sustaining research and development in manned combat aircraft. Congress has repeatedly earmarked money for preliminary bomber studies.

There are two major questions to be answered before research can begin to focus. One is whether USAF leaders are serious about the need for a long-range bomber, or whether they see it as a way to support the Lockheed Martin F/A-22 program by adapting the Raptor into an interim bomber. The other is whether the answer to the USAF’s needs is a manned supersonic bomber at all, or whether the best solution for LRS is a large unmanned aircraft or an ‘arsenal aircraft’ armed with high-speed cruise missiles.

All these solutions are still on the table and the subject of current and future studies. The F/B-22, conceived directly after 11 September, is still the only specific program that USAF leaders have mentioned in public. The Defense Advanced Research Projects Agency (DARPA) is working on plans for a large, manned prototype of a multipurpose blended wing/body (BWB) aircraft for bomber, cargo and refueling missions, and there are at least three technology demonstrations in progress aimed at high-speed cruise missile applications.

Furthermore, NASA – which has scaled back its own hypersonic work and left the field to the military – is showing renewed interest in supersonic-cruise technology and is working with industry on plans for a demonstrator that would support military and commercial applications.

The supersonic-cruise technology being studied today originated in the late 1990s. At that time, Boeing, McDonnell Douglas, General Electric and Pratt & Whitney were involved in the large and growing NASA High-Speed Research (HSR) program, aimed at developing technology for a 300-seat, 350t M2.4 commercial transport. HSR ended abruptly in early 1999 when Boeing – which had absorbed McDonnell Douglas and was consequently the only industry partner for the HSR airframe – presented NASA with a new market assessment that showed that the aircraft would not be economically acceptable.

At around the same time, Lockheed Martin had been working on more advanced supersonic technology that pointed to the feasibility or building a smaller supersonic aircraft – in the 50-60t class – which would be more efficient and would not leave an audible boom track on the ground. Lobbying by Lockheed Martin and Gulfstream, which briefly teamed with the former company to look at a supersonic business jet, led to the start of DARPA’s Quiet Supersonic Platform (QSP) program.

Military focus

DARPA originally hoped to select a contractor team for a flight demonstration program in 2003, but this did not happen. After 11 September, DARPA was directed to focus on military needs rather than dual-use military/commercial projects – the USAF did not consider supersonic cruise to be a priority at that time. QSP’s goals were also very ambitious – DARPA wanted a 45t aircraft to fly 11,000km with a 9t payload – and could not be met without the use of very advanced technology. In the process, however, QSP answered some important questions and pointed the way towards a practical supersonic-cruise vehicle.

Northrop Grumman has been the most visible supporter of an all-new future supersonic bomber. Very early in QSP, Charles Boccadoro, the company’s program manager, said that internal work before the program began had shown the advantages of a bomber cruising at M2.4. “Response time, and cost per target killed, were the two holy grails,” Boccadoro commented in early 2001. Even using NASA’s HSR technology, with a conservative aerodynamic configuration and fixed-cycle engines, a supersonic bomber was comparable in cost to a subsonic aircraft such as an updated and simplified B-2: the supersonic aircraft was bigger and more complex, but the sortie generation rate was far higher and fewer aircraft were needed. “It is as lethal and the first hit comes sooner,” Boccadoro commented.

Supersonic survivability

The supersonic aircraft was also more survivable against advanced threats, due to its high operating speed and altitude and also because it could use relatively inexpensive, unpowered glide weapons with a substantial stand-off range – estimated at 170km from a M2 launch. However, the primary reason for supersonic speed is not survivability – as was the case with the XB-70 and B-58 supersonic bombers – but the ability to respond quickly and increase the sortie rate.

From the outset, Northrop Grumman has focused on configurations that combine high performance with flexibility. The reason that the B-2 is relevant today, Boccadoro notes, is that it has a larger internal capacity than USAF planners originally wanted: “You don’t want to develop something that is completely dependent on a single type of weapon.” The company is also stressing designs that can loiter at subsonic speeds for an extended time before accelerating to supersonic speeds to engage a distant target or evade a threat.

Under QSP, Northrop Grumman carried out two main programs. The company has developed technology and configurations for more advanced supersonic aircraft. Northrop Grumman is still focusing on speeds in the M2 regime, because work to date has shown that faster aircraft would be more difficult to support: an M2 aircraft can be relatively conventional in terms of materials and systems, because structural hearing does not drive the design. “We did not want to pick a Mach number where we could not fall back on aluminum,” says Boccadoro.

The company’s more recent designs include unconventional features such as highly swept, high aspect-ratio wings strut-braced to the rear fuselage. The goal is to achieve laminar flow over the wing, substantially reducing drag: it is easier to maintain laminar flow if the wing chord is short, because there is less time for turbulence to form and propagate through the airflow over the wing. Bracing the very slender wing reduces weight.

With the very slender wing, most of the fuel is carried in the fuselage fore and aft of the weapon bay. Northrop Grumman’s supersonic-cruise designs are very long and slender, and the wing lift is spread smoothly along the length of the aircraft. Both these features help the designers to reduce the sonic boom, the primary goal of QSP and the focus of Northrop Grumman’s other QSP-related efforts.

Low sonic boom theory dates to the early 1970s, but it has taken the advent of higher-powered computational fluid dynamics (CFD) technology to make it a practical approach to aircraft design. The challenge in low-boom design is that the shockwave changes shape as it moves away from the aircraft; more powerful CFD makes it possible to model the airflow for several body-lengths around the aircraft, giving the designer an accurate idea of the way in which the wave develops.

A team led by Northrop Grumman demonstrated low-boom technology in flight for the first time in August 2003, using a modified F-5E fighter. The aircraft was fitted with a large nose fairing which was designed to flatten the front part of the N-shaped shockwave. The goal of the test was not only to prove that the technology would work, but also to show that its effects would persist through the atmosphere to the ground. In the August tests, the modified aircraft was followed 45 seconds later by a standard F-5 flying at the same speed and altitude on the same track. The results were very close to the predictions.

Commercial requirements were the original reason for pursuing low sonic boom designs, but Boccadoro argues that the discipline is equally essential for a military aircraft, both in deployment and training: realistic training for a long-range supersonic cruise aircraft will mean flying long supersonic missions which cannot be accommodated in the relatively small areas that are open to military supersonic flying today.

Low-boom probably sets a practical upper limit to the size of a future strike aircraft – meshing with Air Force Secretary Roche’s vision of a regional rather than intercontinental bomber. “If you get to 110t it’s harder to keep the boom shape,” Boccadoro says.

Other airframe companies have studied supersonic-cruise bombers but have not directly discussed their work. Boeing has shown concepts of supersonic business jets – which would be in the same size class as a regional bomber – that belong to the same family of designs as the Sonic Cruiser near-supersonic airliner that the company attempted to market in 2001-02. The dark horse – not surprisingly – is the Lockheed Martin Skunk Works at Palmdale.

Low boom project

Lockheed Martin has been a participant in QSP, but since 2001 the company has been working on a second low-boom supersonic project parallel to QSP, at least as large in size, focused on nearer-term goals and protected by tight security. That project’s first goal is to develop technology for a supersonic business jet, and it is funded by an outside sponsor: either a corporation or a wealthy individual. The program manager, Tom Hartmann, has only given one interview about the project, in August 2003, and subsequent requests have been turned down. One reason given by Lockheed Martin for its reticence – not that secrecy is unusual for the Skunk Works – is that the project is related to military activities.

In a November 2003 briefing to the Federal Aviation Administration, Lockheed Martin gave some clues to its technological approach. The company showed a design for a 60t, 40m-long aircraft with a sharply swept wing, braced by an inverted V-tail to the rear fuselage. The aircraft would have a conventional low-cost structure, simple inlets and conventional turbofan engines, and would take advantage of supersonic laminar flow. Lockheed Martin is also looking at shock cancellation – in effect, generating pressure waves at certain points on the surface to cancel out other shocks.

Lockheed Martin, remarkably, describes low-boom technology as “demonstrated” and its design as “closed”. This is in sharp contrast to Northrop Grumman: Boccadoro says that there is a need for a “JAST- [Joint Advanced Strike Technology] type program”, a large, focused effort to bring new technology to a point where it is mature.

With all these activities under way, it is not surprising that General Electric’s (GE’s) manager for advanced technologies, Harvey Maclin, expects the coming year to be “interesting”. Maclin’s team at GE is supporting the Lockheed Martin and Northrop Grumman efforts, as well as several other teams looking at supersonic business jets.

GE is working on an advanced variable-cycle engine for supersonic-cruise aircraft. Its key feature is the ability to adjust its bypass ratio and fan pressure ratio to provide low noise on take-off, subsonic efficiency for loiter, maximum thrust for transonic acceleration and best efficiency in the cruise. The key, Maclin says, is an engine core that adapts to different flight conditions.

NASA’s supersonic vehicle sector manager, Peter Coen, says that the agency is defining a purpose-built supersonic demonstrator that Maclin believes could be flying in 2007, powered by modified GE F110 fighter engines, if funds are made available soon enough. Coen says that NASA is thinking of a long-life “modular” X-plane that could be used to test a set of technologies, then grounded and modified for a different series of tests. For example, the first configuration might be designed mainly for a new series of low-boom tests: unlike the F-5 trials, the goal would be to reduce the front and rear shocks, and convince governments and the public that low-boom aircraft could be acceptable overland. After that, the demonstrator could be modified to test supersonic laminar flow technology, or used to test more advanced end efficient engines.

A regional bomber based on new supersonic technology would be more expensive than the F/B-22 but much more capable. The F/B-22 has an unrefueled range of 3,000km, according to USAF Chief of Staff General John Jumper, combined with “some ability to supercruise” over hostile territory. It would still require extensive tanker support to operate from bases outside the immediate area of operations and, if it cannot cover long distances at supersonic speed, it will offer few advantages in sortie rate compared with today’s bombers. Also, most discussion of the F/B-22 has suggested that it will have a stretched body compared to the F/A-22, with internal bays for 30-plus GBU-39/B Small Diameter Bombs, but it will not be able to carry large weapons internally – even the 900kg JDAM – unless it is heavily redesigned.

Another alternative approach, the “arsenal aircraft”, is probably more of a complement than a competitor for a supersonic regional bomber. DARPA’s vision of the Modular BWB/Multi-Role Aircraft (MRA) is a very efficient subsonic platform with at best a moderate level of stealth. Its most revolutionary attribute will be its ability to be reconfigured in the field to perform cargo or tanker missions or to launch cruise missiles or unmanned aerial vehicles. DARPA also sees the BWB in electronic warfare missions, carrying very large antennas in its wings.

The BWB MRA could support prompt strikes if it were armed with high-speed missiles. Currently, there are three technology programs in that area. The US Navy/DARPA HyFly program uses a dual-combustion scramjet engine. The team has conducted more than 80 successful ground tests since May 2002, and a powered flight test is expected in the first half of 2005. The goal is a missile with an 1,100km range at M6.

The Office of Naval Research, meanwhile, is sponsoring a project called RATTLRS (Revolutionary Approach To Time-critical Long Range Strike): this is a high-supersonic missile, with a speed between M3.5 and M4.5, powered by a Williams International turbojet engine. First tests could be as early as 2006.

The third effort is the Single Engine Demonstration (SED), an offshoot of the ATK/Pratt & Whitney hydrocarbon scramjet work that has been sponsored by the USAF and NASA since the early 1990s. However, while such weapons can play an important role, they are always likely to have a high cost per target relative to unpowered weapons launched from a bomber.

Technological progress

Overall, a supersonic bomber may be the best approach to combining promptness, high sortie rate and a low cost per kill, while reducing the USAF’s dependence on bases within 1,000km of its targets. The concept’s future is far from certain in an atmosphere of financial, military and political uncertainty, but for the time being it appears to be gathering support, thanks to operational needs and signs of technological progress.

That the USAF needs a new bomber is not surprising, since the service has not ordered any new bombers in more than 20 years and its last bomber program was cut back to a handful of very expensive, marginally sustainable platforms. The current fleet comprises 157 aircraft: 60 B-1s, 21 B-2s and 76 B-52Hs. Some of these aircraft are assigned to training or testing or are, at any time, being maintained, leaving 36 ‘combat-coded’ B-1s, 16 B-2s and 44 B-52Hs.

The B-52H – the last of which was delivered 42 years ago – is undergoing what the USAF calls the Avionics Midlife Improvement (AMI) program. AMI is an upgrade to the B-52’s Offensive Avionics System (OAS), which was fielded along with the AGM-86B Air-Launched Cruise Missile (ALCM) in the 1980s and is now becoming impossible to support. Under AMI, the inertial navigation system, the central avionics control unit computer and the data transfer system – described as “Commodore 64” technology, and approaching the point of being impossible to support – are all being replaced by off-the-shelf modern hardware, hosting a combination of new and adapted software. As well as improving failure rates and reducing support costs, AMI is the foundation for other new capabilities, including advanced extremely high-frequency (AEHF) wideband satcoms and datalinks. An 80-sortie flight test program began in December 2003 and was completed in March 2004.

New weapons for the B-52H included the Lockheed Martin AGM-158 Joint Air-to-Surface Standoff Missile (JASSM), which reached initial operating capability on the bomber in October 2003. It will also be the first USAF aircraft to carry the winged Wind Corrected Munitions Dispenser – Extended Range (WCMD-ER).

Another new capability for the B-52 was used operationally in Iraq in April 2003, when a B-52H released two GBU-12 laser-guided bombs and guided them to impact with a Rafale Litening targeting pod: the first use of any laser designation system on a bomber.

One option for the B-52H that is still under study – as it has been since 1982 – is a re-engining program. Since the advent of the first commercial high-bypass engines, it has been clear that a new engine would improve the bomber’s performance and reliability and reduce the cost of fuel and maintenance, and repeated investigations have shown no insoluble problems in going from eight engines to four. However, the USAF has turned down repeated proposals to carry the program out, for reasons that have more to do with government financial rules than with common sense: unlike a business, the air force cannot recover a capital expense from reduced operating costs.

Moreover, the USAF’s last thumbs-down – when it rejected a 1996 modernization proposal from Boeing and Rolls-Royce – turned out to be based on poor data. Although the service has large stocks of TF33 engines, it underestimated their maintenance costs and, amazingly, did not take account of the fact that a re-engined aircraft would need less tanker support: fuel that costs a dollar a gallon on the ground costs US$17.50 out of a tanker’s boom.

Re-engining study

A 2002 Defense Science Board (DSB) report advised the USAF to conduct a new study of a re-engining program, which was completed in 2003. The leading candidate engines are still the Pratt & Whitney PW2037 and Rolls-Royce RB211-535, but the study was broadened to include a configuration with eight Pratt & Whitney JT8D-200 engines – which would offer less performance but would avoid changes to the rudder system.

On the Boeing B-1B, the USAF is engaged in a battle of wills with Congress. Before 11 September, Air Force Secretary Roche and Chief of Staff Gen Jumper announced a plan to retire one-third of its B-1Bs – 32 aircraft – to fund improvements to the rest of the aircraft and to allow them to be supported properly. The project was a success, according to Roche. “We took a system that people thought was worthless”, he says, and brought it to the point where it could fly 2,300km to a target in 2.5 hours, deliver 24 JDAMs and return with a single refueling.

“It worked so well,” Roche adds, “that Congress has told us to bring them [retired aircraft] back, even though some of them will come back on flatbed trucks.” Congress has directed the USAF to return 23 of the aircraft to service; the USAF says that it cannot afford to continue improvements to the force in that event. In April, Gen Moseley advised Congress that the USAF could support seven more B-1Bs without prejudice to its other operations.

The current B-1 standard is known as Block E. It incorporates improvements such as integration between the GPS navigation system and the ground moving-target indicator (GMTI) and synthetic aperture radar (SAR) modes of the Northrop Grumman APQ-164, communications improvements and the ALE-50 towed decoy. Already operational with JDAM, the B-1B is due to receive WCMD and JASSM.

The B-1B should also be the first platform for the AGM-158B JASSM – Extended Range (JASSM-ER). Phase II development of JASSM-ER started under a contract awarded in February 2004 and includes flight tests, which start in mid-2006. Production missiles should be available in 2008. Externally identical to the AGM-158A, the longer range missile has a larger fuel load and a more powerful and efficient engine – USAF documents indicate that a lower-cost version of the Williams International F107 was one candidate for this role in 2002 – and a range of more than 900km.

The third bomber in the USAF fleet, the Northrop Grumman B-2, was declared fully operational in December 2003, 22 years after the development contract was awarded and 10 years after the first Block 10 aircraft was delivered to the 509th Bombardment Wing at Whiteman Air Force Base (AFB). During the 2003 Iraqi campaign, B-2s flew their first combat missions from a base other than Whiteman. Portable shelters were set up on the island of Diego Garcia in the Indian Ocean, permitting maintenance crews to test and repair the bomber’s low-observable (LO) materials; four B-2s were deployed, performing 43 missions and releasing 400 precision weapons, including 13 GBU-37/B 2,540kg hard-target bombs.

The B-2 is now being tested with new weapons, including JASSM. The EGBU-28 is in the same size class as the GBU-37/B, but uses the standard JDAM tailkit rather than the GPS Aide Munition (GAM) guidance system on the earlier weapon. Also becoming operational is the Smart Bomb Release Assembly (SBRA), which allows the B-2 to carry and release up to 80 individually guided, 225kg-class GBU-38 JDAM-82 guided bombs. The first series of 80-bomb test launches was completed in September 2003, with weapons being released at Hill AFB, Utah. Northrop Grumman was awarded a production contract for the SBRA – which is a modification of the original non-rotating stores rack – in May, and the retrofit program is due to be completed in the first quarter of 2006.

The B-2 will also be essential if the USAF follows the recommendations in the DSB’s report on strategic strike, issued earlier this year. The DSB concluded that current USAF penetrator weapons would be ineffective against deep tunnels. The report advised the Pentagon to start immediately on demonstration of a massive bomber-delivered penetrator, weighing 9,000-14,500kg. The B-2 is likely to be the most suitable platform for such a weapon.

Other alterations have improved the B-2’s performance since Operation ‘Iraqi Freedom’, including more effective over-the-horizon communications and the ability to download a complete mission plan in flight via a Link 16 datalink. A larger, centrally mounted display is being installed in the bomber’s cockpit to help in mission planning. In April 2004, the long awaited alternate high-frequency material (AHFM), a paint-type material that eliminates 3,000ft of tape currently used to seal access panels, was applied to an operational aircraft for the first time: that aircraft will be returned to service later this year.

Unique asset

Two other substantial changes are in progress for the B-2. Under a November 2002 contract, Raytheon is developing a new X-band active electronically scanned array (AESA) for the B-2’s APQ-181 radar. There are no problems with the radar itself, which was developed at great cost and uses a passive ESA; the problem is that the Pentagon – for reasons which may well have been rooted in secrecy – failed to reserve the APQ-181 frequency (in the Ku-band) with either US or international regulators. This bandwidth was auctioned off in the early 1990s and is likely to be become heavily populated with commercial devices. The new antenna is expected to cost US$900 million and installation will be carried out between 2007-10.

Another major effort could involve fixing the area immediately behind the engine exhausts of the B-2, known as the aft deck. Structural problems in this area, caused by heat and acoustic vibration, were identified very early in the program and although repair schemes have been devised and implemented, the basic problem has never been fixed. At one point, in early 2002, six B-2s were described as “en route to being non-flyable” because their aft deck sections were damaged to a point where their LO characteristics were compromised.

An urgent repair scheme was devised by Northrop Grumman, the USAF program office and the Air Force Research Laboratory, and released to the fleet by mid-2003. The AFRL has also been enlisted to help find the root cause of the cracks and devise a more permanent repair.

For the USAF, the B-2 is both a unique asset and a problem. There is no other aircraft with a comparable ability to deliver heavy weapons or many independently guided weapons against defended targets with a comparable chance of survival. On the other hand, the B-2’s unique, specially developed and often quite dated technology makes operations very expensive, while the small size of the fleet limits the total operational pay-back for any investments.

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