A stealth B-21 and B-2, top, penetrate an adversary’s air defenses as a B-1B and B-52 launch long-range strike weapons from standoff distances and a pair of hypersonic missiles launched from over the horizon close on their targets. Mike Tsukamoto/staff; photos USAF
Photo Caption & Credits

Stand In, Standoff

The Right Balance for the Future Bomber Fleet.

America’s global interests are threatened like never before. China and Russia now pose security challenges that the United States has not confronted since the Cold War—some potentially existential in nature. At the same time, mid-tier powers like North Korea and Iran now have ballistic missiles and aspire to develop the ability to deliver nuclear warheads over long ranges. Added to this, non-state actors such as al Qaeda, the remnants of the Islamic State group, and Hezbollah continue to plot attacks against the United States and its allies. The concurrency of these threats has stretched American military resources to their breaking point. With vital interests on the line, U.S. leaders must ensure the U.S. military is equipped to deal with the weighty demands of national defense strategy. 

Global long-range strike—the ability to attack targets anywhere, at any time—must be among our highest priorities. When paired with an effective campaign strategy aimed at vital targets on which an enemy’s military depends, long-range strike is one of the most effective tools available to America’s military commanders. 

History offers clear proof. After Allied forces stormed the beaches of Normandy in June 1944, it took just 11 months to reach Berlin and put an end to the war. In contrast to World War I, when that very same territory bogged down opposing armies in bloody trench warfare from 1914 to 1918, Allied long-range strike bombers reduced Germany’s ability to sustain combat operations on the ground, in the air, and at sea. In the Pacific, long-range strikes executed by 20th Air Force B-29s and two atomic airstrikes achieved unconditional victory without a costly invasion of Japan’s home islands. 

Since then, precision guided munitions (PGMs), improvements in aircraft range, and stealth technologies radically enhanced what combat aircraft could achieve in the battlespace. Today, one stealth B-2 sortie can strike 80 individual targets with pinpoint accuracy—without needing accompanying support aircraft to assure it survives. 

Long-range strike follows one of two approaches: Stand-in strikes employ stealth aircraft to penetrate enemy defenses and release munitions in proximity to targets, while standoff strike attacks target from a distance by launching long-range missiles, either from aircraft, ships, submarines, or land.

Each has strengths and weaknesses, with recent debates pressing to go “all-in” on investments for one or the other. Today, the Army and Navy are starting to bolster their strike capacity by procuring new long-range standoff missiles. These investments are often viewed as a panacea for anti-access, area denial (A2/AD) defensive strategies used by our adversaries. Yet, it is simplistic to think that lobbing a missile at range will negate A2/AD challenges, and doing so puts at risk other options available to U.S. commanders. 

A key insight from post-Cold War government and non-government analyses is that both standoff and stand-in strike capabilities are necessary. Air Force Chief of Staff Gen. David L. Goldfein recently noted that after a significant number of USAF wargames, the force that wins in Defense Department planning scenarios “has a combination of that which works from inside and that which works from outside … a balance” of penetrating and standoff strike forces. Goldfein continued: “As I’ve shared with other leaders who have talked about just shifting to an all-outside force … show me your analysis, this can’t be a gut feeling for us in terms of investment.” 

The Air Force is the only service that operates long-range, penetrating bombers. America’s allies do not have such aircraft. While DOD can depend on a range of standoff strike options from other services and allies, this USAF capability is unique, making it imperative that DOD adequately size and modernize the Air Force’s penetrating bomber force, considering today’s force of only 20 stealth B-2s is woefully inadequate. At the same time, it is also important to maintain the Air Force’s standoff bomber force, which is now sized about right, but whose B-1s and B-52s must be modernized. 

The Long-Range Strike Arsenal

America has long relied on the Air Force’s bombers to rapidly project power globally, but the bomber force is aging. USAF’s 76 B-52Hs, 62 B-1Bs, and 20 B-2s—158 planes in all—constitute the oldest and smallest bomber force since the branch’s founding in 1947. Multiple studies have concluded the United States cannot generate enough long-range strike sorties for a single major conflict with a peer adversary, recommending a force roughly 50 percent larger, with at least 220 bombers. B-21s, now in development, must constitute the bulk of this modernization effort. B-21s represent the next generation of stealth—a fifth-generation-plus bomber in which sensors, processing power, stealth, and connectivity deliver a powerful mix of mutually reinforcing capabilities. 

While current plans call for at least 100 B-21s, there is also lingering interest in a new nonstealth, standoff platform that some believe could cost less than the B-21s. Some have suggested the Air Force could either modify existing cargo aircraft to launch cruise missiles or develop a new, clean-sheet standoff “arsenal plane.” Neither of these options would be cheaper than procuring additional B-21s, nor is it likely that a new standoff bomber could be fielded faster than the B-21 program can achieve full-rate production. More importantly, seeking to rebuild the bomber force with arsenal planes could reduce long-range strike options available to theater commanders in the future, as well as wasting resources by overinvesting in standoff strike capacity, which other services also intend to procure. Simply stated, money directed to standoff aircraft will limit the Air Force’s ability to overcome its more significant deficit in long-range, stand-in strike capacity. 

At the end of the Cold War, the Air Force’s bomber force totaled about 400 aircraft. In the ensuing years, budget cuts and confidence that a much smaller bomber force would suffice for conflicts with rogue states such as Iran and North Korea led to reductions, including DOD’s 1997 decision to cap the B-2 program at 21 aircraft instead of the 132 B-2s sought by the Air Force. Bomber cuts continued into the 2000s when the Air Force retired an additional 33 percent of its B-1Bs and 20 percent of its B-52Hs. These retirements continued even as demand for bombers surged, with DOD’s bomber fleet tasked with nonstop deployments. This hard use literally broke the B-1 fleet in 2019. 

Now facing budget challenges akin to the 1990s and early 2000s, the Air Force wants to retire another 17 B-1Bs to help free-up funding to sustain its remaining bombers,  according to acquisition chief Will Roper and Deputy Chief of Staff for Plans and Programs, Lt. Gen. David S. Nahom in testimony to Congress in February. This would leave 45 B-1Bs in the force, of which an estimated 26 will be primary mission aircraft assigned to combat squadrons. We have been down this path before. Chronic underfunding of sustainment and modernization after the Cold War led to divesting older bombers to free resources to sustain the remaining aircraft. Then, even as these additive resources disappeared over time, the remaining bombers were flown harder to meet operational requirements. The toxic combination led to more bomber sustainment challenges, which drove the next round of force cuts. The arguments made today to rationalize B-1 cuts are the exact same as those made in the early 2000s justifying the retirement of two dozen B-1s. 

The Air Force’s budget-driven choices today will create a period of increased risk in its ability to conduct long-range strikes. The B-21 program is the first opportunity to correct its overall lack of bomber capacity and standoff/penetrating strike imbalance. Yet it will take time to offset 30 years of bomber divestments and delayed modernization. Assuming B-21 production ramps to a modest five to 10 aircraft per year by the late 2020s, fewer than 40 B-21s could be on the ramp by 2030. At this rate, it would take another decade before the Air Force gains back the number of bombers it is surrendering today. It will be well into the 2040s before it reaches its stated requirement for at least 220 total bombers. If the B-21 is delayed by budgetary or technical challenges, USAF’s bomber bathtub could be even deeper and last longer. 

Prioritizing Penetrating Capability

DOD is now faced with a set of challenges that are radically different than the regional threats it confronted over the last 30 years. Defeating Chinese or Russian forces that are operating under the umbrella of integrated air defense systems (IADS) and other anti-access, area-denial threats will require U.S. forces to go on the offensive “from the very beginning of hostilities.”  USAF stealth bombers must be able to penetrate these contested areas on Day One of a conflict; taking multiple weeks to build up a ground force before launching a counteroffensive in a war with China or Russia would cede them the time and freedom they need to prevail. The failure to invest in the right capacity and mix of capabilities could be devastating.  

Both long-range standoff and penetrating strikes can be effective against targets in contested areas—but not equally so. Like penetrating systems, standoff bombers can deploy within hours to launch long-range weapons. These platforms can also reduce U.S. force attrition early in a fight when enemy defenses are at full effectiveness. 

In comparison, stealth aircraft can penetrate contested areas and approach targets closely enough to deploy short-range, standoff and direct attack weapons. These munitions are smaller than long-range standoff weapons that have ranges greater than 400 nautical miles (nm). To fly long ranges, weapons typically need power plants, wings that deploy after launch, one or more guidance systems, and other design features that increase their size. As size increases, the number of weapons an aircraft can carry decreases. A B-2 can carry 80 short-range Small Diameter Bombs (SDBs) or 16 much larger Joint Air-to-Surface Standoff Missile-Extended Range (JASSM-ER) weapons. With fewer weapons per sortie, theater commanders need either more time or aircraft to achieve desired effects, time that an enemy can use to press its advantage or even prevail. A future force mix weighted toward penetrating bombers would increase weapons available per sortie, helping theater commanders achieve a decisive advantage. 

Three U.S. Air Force B-21 bombers fly over Fiery Cross Reef, a Chinese People’s Liberation Army base in the South China Sea in this illustration. Mike Tsukamoto/staff; photo Greg Davis; map Google Earth

The potential for weapons to be intercepted or rendered ineffective by enemy defenses is also a factor. China, Russia, and other potential adversaries have developed countermeasures, such as layered air defenses that can intercept incoming weapons; increasingly mobile ground-based systems that are harder to locate and track; and bunker-style installations buried deep underground to make them harder to locate and destroy. 

B-52s are envisioned carrying four AGM-183A Air-launched Rapid Response Weapon (ARRW) hypersonic missiles, as shown in this photo illustration. Lockheed Martin

In the past, the probability that a weapon would be intercepted after launch was small. During the 2003 Operation Iraqi Freedom air campaign, coalition air forces used an average of 1.5 precision guided munitions (PGMs) per target. But today, advanced Chinese and Russian defenses can track legacy cruise missiles and other weapons, making it possible to intercept and defeat them. In this contested environment, three, four, or more PGMs may be needed to ensure at least one survives to hit a designated target, meaning the total number of weapons—and aircraft—needed to attack tens of thousands of targets in a peer conflict would be far greater than DOD can afford to procure. 

While enemy countermeasures increase the number of weapons needed to strike targets from all ranges, they have a greater impact on long-range, standoff weapons. Launched from 500 to 800 nautical mile (nm) standoff distances depending on the threat environment, these weapons must fly hundreds of miles through enemy defenses before they hit a target, increasing the probability they will be detected and intercepted. By contrast, direct attack weapons with flight times of just a few minutes reduce an enemy’s ability to respond. 

From long-range, standoff distances, it is also more difficult to find, fix, track, target, engage, and assess mobile/relocatable targets such as missile transporter-erector-launchers (TELs). A subsonic (Mach 0.8) long-range, cruise missile launched 500 nm from a target would need nearly an hour to reach it, affording an enemy the time needed to detect and stand off attacks and simply change locations. Penetrating aircraft with on-board sensors and other capabilities are better suited to complete the entire kill chain against such time-sensitive targets.

Standoff weapons are also too small to kill targets that are structurally hardened or deeply buried, while penetrating bombers can deliver very large, direct attack weapons specially designed to kill such targets. For instance, a B-2 can deliver 5,000-pound direct attack “bunker buster” weapons and even the 30,000-pound GBU-57A/B Massive Ordnance Penetrator on hardened targets. It is simply impractical to design air-launched weapons with comparable weights to fly very long distances. 

The problem grows with distance. A bomber that must stand off 800 nm from the Chinese coastline would need weapons with more than 1,600 nm range to attack targets located 800 nm inland — well outside the reach of a JASSM-ER with a range of over 500 nm. Standoff distances would be a major constraint in a war with China or Russia, considering the scale of their landmasses and ability to deploy ballistic missile launchers, anti-satellite weapons, and other high-value assets deep in their interiors. 

Then there is the matter of weapon cost. Affordability is a critical consideration, given potential requirements to attack tens of thousands of aimpoints in a conflict with China or Russia. As a point of reference, Allied air forces attacked about 40,000 aimpoints during Operation Desert Storm against a third-rate Iraqi military. Target lists in a war with China or Russia would be much greater. A future force that must use tens of thousands of very long-range, standoff weapons—each costing $1 million or more—is not affordable.

While some suggest the cost of long-range weapons could be offset by buying less-costly standoff aircraft, this is not borne out by analysis. A 2010 RAND Project Air Force study by Thomas Hamilton, “Comparing the Cost of Penetrating Bombs to Expendable Missiles over Thirty Years: An Initial Look,” concluded that a penetrating bomber delivering direct attack weapons for at least 20 days, over a 30-year period, would actually cost less than expending an equivalent number of more expensive standoff cruise missiles.  To put this in context, 20 days of airstrikes is less than half the length of the 43-day Desert Storm air campaign and is far less than the combined duration of all U.S. air campaigns over the past 30 years. This finding was instrumental in DOD’s decision to begin the B-21 program. The cost crossover point would be even more in favor of penetrating bombers if the price of a new standoff aircraft is included in the comparison. Assuming that buying and sustaining a new standoff bomber would run into the hundreds of millions of dollars, the crossover point could be as short as 10 days of combat. In this light, investing in penetrating bombers instead of additional standoff strike capacity is a bargain.

Maintainers assigned to Whiteman Air Force Base’s 509th and 131st Bomb Wings in Missouri watch a sunset near a B-2 Spirit Stealth Bomber, Oct. 24, 2019. Stealth provides the penetrating capability to launch direct attacks in the face of anti-air defenses. Senior Airman Thomas Barley


Assessments to determine USAF’s future, long-range strike requirements must consider the effectiveness, as well as the cost, of using standoff and penetrating weapons against very large peer adversary target sets in contested areas. As noted by Marine Corps Commandant Gen. David Berger: “There is an argument to be made by some who feel that two great powers can stand off with long-range precision weapons and hold each other at bay. … I am not in that camp.”  

In the end, it comes down to how the Air Force should invest its finite budget to field the most effective and efficient set of capabilities to support the National Defense Strategy. To this end, the Mitchell Institute offers the following recommendations:

The Air Force should significantly increase its long-range strike capacity. A total inventory of at least 316 bombers is needed to support the U.S. National Defense Strategy, the vast majority of which should be penetrating aircraft. DOD’s 1997 decision to stop buying stealth B-2s created a bomber force that is now too small, too old, and overweighted toward standoff aircraft. This force was adequate against lesser regional militaries in the past, but in contested conflict with peer adversaries, it will not be sufficient. The Air Force must buy at least 240 B-21 stealth bombers. 

Long Range Strike Sorties

The Air Force should prioritize penetrating strike platforms. Success in warfare comes down to inflicting rapid, overwhelming attacks against key targets. Sustaining such operations demands an affordable means to conduct strikes. Today’s B-1Bs and B-52Hs cannot penetrate Chinese or Russian IADS with an acceptable degree of risk, nor can any nonstealth aircraft. Without the ability to penetrate, bombers must launch standoff weapons from hundreds of miles away, delaying impact and reducing effectiveness against relocatable targets. These weapons are smaller, lack the warheads capable of destroying hardened or deeply buried targets, and are also more expensive than direct attack munitions. To avoid redundancy, since the other U.S. military services also are investing in new standoff capabilities, the Air Force must ensure it can provide commanders with options to penetrate deep into contested areas and strike a large number of targets per sortie. 

Hypersonic weapons are needed but will not be a panacea. Advanced integrated air defenses will be effective against legacy subsonic cruise missiles as well as nonstealth aircraft, making hypersonic (Mach 5 or greater) weapons attractive. Due to their high speeds, maneuverability, and other characteristics, they will be better able to survive high-risk threat environments. These more survivable weapons could reduce the total number of standoff weapons needed to attack defended targets. However, hypersonic weapons launched from standoff distances will still be less effective against mobile targets than direct attack PGMs that can reach targets in minutes. Hypersonic weapons will also be expensive. Like other standoff munitions, investments in hypersonic weapons should be informed by tradeoffs between survivability, size, weapons per sortie, and effectiveness against challenging targets—in addition to cost.

Allocating modified airlift aircraft to conduct strike missions does not make operational sense. There are already indications of a growing shortfall in the Air Force’s capacity to provide heavy airlift to rapidly deploy and sustain forces. Allocating some number of modified airlifters to conduct strike missions instead could have a major impact on the U.S. military’s ability to prevent China or Russia from achieving a quick victory. 

Mitchell Institute

Developing a new standoff bomber is not a quicker or cheaper option. The notion that a new, standoff arsenal aircraft with large payload capacity could be developed quickly and at less cost than buying the B-21 is a myth. Restarting a production line for a military airlifter like the C-17 would require years and billions of upfront investment. Modifying a C-17 or existing commercial cargo aircraft to carry standoff weapons would also require even more funding and time. Consider the effort needed to develop the Navy’s P-8 maritime patrol-strike aircraft from a commercial design and continued struggles surrounding the Air Force’s KC-46A tanker: The resulting cost of a weapons-carrying, wide-body aircraft could equal or exceed the B-21’s cost, while providing a less operationally flexible, single-mission capability. It is likely that a clean-sheet design, standoff bomber would be even more expensive than a program that modifies a mature airlifter to launch weapons. 


America’s penetrating long-range strike force today consists of 20 stealth B-2s—the rest of the bomber force and all of the other services are limited to launching long-range strikes from outside contested areas during a conflict with a peer adversary. This reality invites China and Russia to field even longer-range air defenses that would drive USAF’s nonstealth bombers and other aircraft further out in the battlespace. This in turn would require the Air Force to invest in new standoff weapons with even greater ranges and higher price points. Continued reliance on too much standoff strike capacity would create opportunities for peer competitors to invest in capabilities that would impose costs on the United States.

A force of at least 316 bombers is needed to support the U.S. National Defense Strategy. This force should consist of 76 B-52s and at least 240 fifth-generation B-21s. The choices made in coming years will fundamentally shape how our military will operate against great power aggressors. Long-range, penetrating strike bombers expand policy options, strengthening the hand of American leaders. Without this force, the United States will be at a severe disadvantage against peer competitors.         

Col. Mark Gunzinger USAF  (Ret.) is the director for future aerospace concepts and capabilities assessments at the Mitchell Institute for Aerospace Studies. This article was adapted from a Mitchell report entitled “Long-Range Strike: Resetting the Balance of Stand-in and Stand-off Forces.” For the full report, visit https://mitchellaerospacepower.org.