Smaller Bombs for Stealthy Aircraft

July 1, 2001

In 1999, the US Air Force faced a war over Kosovo that was very different from the Persian Gulf War almost a decade earlier. Foul weather regularly hindered attack aircraft, while enemy air defenses kept fighters at high altitude. Hidden, mobile targets were difficult to locate and destroy.

Further complicating Allied Force was the dense urban environment of Belgrade, the Serbian capital, which was the focus of many US attacks. In the attempt to end Serb aggression against Kosovo, collateral damage became a large concern, as military targets were often located among civilians.

After the war, the Air Force determined that Allied Force validated USAF’s push for smaller and more accurate weapons. The need to destroy specific targets in populated areas showed the value of precision attack.

In addition, using a smaller bomb to destroy a target by delivering it precisely on target fit into USAF’s increasing emphasis on stealth. Today’s F-117 and B-2 stealth aircraft carry their weapons internally to maintain a radar-eluding profile. The upcoming F-22 and Joint Strike Fighter will also have limited space for weapons, if flown in a stealthy configuration without bombs hung from hardpoints on the wings.

“F-22 and JSF still have relatively small bomb bays,” one official noted, “and with precision, it doesn’t take as much raw power to achieve the desired effect.”

The 1997 requirements document that led to current small bomb efforts had this to say: “Internal carriage aircraft … possess a very limited capability to employ multiple weapons per pass with current munitions systems. The munitions addressed by this [mission needs statement] should be independently targetable over a wide area and have multiple carriage capability on aircraft and space delivery platforms, beyond the capability of current munitions.”

The “Key Enabler”

Bruce Simpson, Armament Product Group deputy manager, Eglin AFB, Fla., once noted that miniature munitions are becoming a “key enabler.” Smaller warheads are needed because “JSF and F-22 really need that additional capability,” and during Allied Force, “most targets [that] we were addressing needed less damage than were given to them,” Simpson said.

A senior officer added that the 2,000-pound AGM-130, despite its accuracy, “was often the wrong weapon for Kosovo” because of the potential for collateral damage.

The mission needs statement for a miniaturized munitions capability had already begun the process of creating a new small bomb program when Allied Force took place.

An Analysis of Alternatives completed by Air Combat Command last year determined that each of 26 small, precision weapons evaluated in the AOA offered new warfighting capability for the Air Force, service officials say. The 26 small bomb concepts “all had merit,” reported one senior officer.

These miniaturized munitions trends evolved into what was temporarily known as the Small Smart Bomb program. That program has now become the Small Diameter Bomb-one of the service’s new weapon priorities and a program that is being accelerated from earlier schedules, thanks to support from top Air Force leaders.

The name change was made “to ensure that [SDB] didn’t get associated with a single concept [from the AOA and] to set it aside as the next step,” explained Brig. Gen. Daniel P. Leaf, Air Force director of operational requirements. The new name “emphasizes a couple of things,” he said.

“The small diameter is important because it could be [carried by an Unmanned Combat Air Vehicle], or it could be increasing the weapons capacity of an F-22, a Joint Strike Fighter, or the weapons carriage capacity of a B-2,” Leaf said.

Although the SDB concept is still being developed and no contractors have been selected, service officials estimate the weapon will produce a fourfold increase in the number of independently targetable weapons that stealthy aircraft can carry.

“From my perspective,” said Leaf, “I really like what it does for our stealth aircraft capacity, because as SA-10s and [SA]-20s continue to proliferate, [stealth is] going to be increasingly important, and the only way to be stealthy is to put the stuff inside.”

Future Star

In the words of Maj. Gen. Michael C. Kostelnik, Air Armament Center commander at Eglin: “If we had the [SDB] in numbers in Kosovo, it would have been the star.”

The mission needs statement notes, “Several of the current platforms (such as the F-15E, F-16C/D, F-117, B-1, B-2, and the ballistic missile) and next-generation platforms will be capable of carrying only a limited number of existing and planned munition systems,” which makes miniaturization critical.

These needs include:

  • Multiple kills per pass.
  • Reduced airlift support.
  • Ability to locate and destroy small and mobile targets in real time.
  • Resistance to camouflage, concealment, and deception.
  • Minimal collateral damage.
  • Resistance to countermeasures.

The program also meshes with service desires to better tailor weapon inventories to true requirements. A key finding in Air Force reviews of future weapon plans was the fact that USAF needed to take a harder look at inventories, said Lester McFawn, director of plans and programs for the Air Armament Center. The service must evaluate the efficacy of making one-for-one replenishments as weapons are used and determine whether the service should instead be moving toward future precision weapons that minimize collateral damage, such as SDB, McFawn said.

Everyone agrees that, because precision weapons have been so popular in recent operations, something needs to be purchased to replenish the supplies. And as Leaf said, “We already had some concerns about munitions shortfalls [and SDB] helps us meet it. … It will be a very cost-effective solution.”

In April, the service established an SDB system program office at Eglin, using funds left over from weapon experiments and a Fiscal 2001 increase from Congress.

The SDB program is developing a new, small-payload precision weapon for use aboard almost every Air Force combat aircraft, beginning with the F-15E Strike Eagle, according to SDB Program Manager Terry Little.

From the beginning, USAF officials sought to create a new weapon that would have not only the ability to precisely attack fixed targets but also to go after the more difficult mobile and relocatable targets. A phased approach was selected in order to get the SDB capability into the field while more advanced versions of the weapon are still under development.

“You could almost consider it a four-phase program, if you count 500 [-pound Joint Direct Attack Munitions] as an initial phase,” Leaf said. The service is still pushing for the smaller JDAM, as the larger 1,000-pound variant proved its effectiveness and relatively low cost during Allied Force.

Officials say the goal is to make SDB smaller while giving it a capability that is even greater than the 500-pound JDAM. Still, said McFawn, the Joint Direct Attack Munition was cited as a prototype for future weapons development because it cost much less than early estimates-“and was ready in about half the time of traditional weapons, which often take 12 years to develop.” McFawn said, “The real desire is to do even better than JDAM.”

Ready in 2006

Therefore, Little said, SDB will be developed in stages, with the first capability guided by inertial navigation and Global Positioning System guidance. Phase 1 will be for fixed targets and is scheduled to achieve operational capability in 2006, Little said.

Last year, this capability was expected to become available in about a decade, but since then, the Air Force has funded a faster pace for the program. Col. James Uhle, chief of the weapons division under Leaf at the Pentagon, has observed that it “takes way too long to get [new precision weapons] on our aircraft.”

Responding to this concern, Little said he hopes the SDB program will be in development for four years, much less than the time needed for similar programs in the past. Little said $38 million is needed in Fiscal 2002 to continue the program. The source of that money has not yet been identified, but it likely will come from other Air Force programs.

“Air Combat Command will prioritize, look at what requirements it supplants, and make those trades,” Leaf said. SDB has “very, very high potential–it will be worth making the trades,” he said.

Beyond the weapon itself, the cost of integrating the weapons with the software, carriage, and targeting requirements involved in the certification process can slow weapons programs down, but officials say this certification process is essential for SDB-in order to get the full capability from the weapon.

“Integration into the aircraft, and making sure we get all the capability out of it–that’s going to be key,” Leaf said.

SDB Phase 1 will provide the ability to attack fixed targets with a common carriage system. The smart multiple ejector rack will be used to integrate SDB onto aircraft, and according to Air Armament Center commander Kostelnik, prototype racks have already been demonstrated.

Phase 2 will focus on going after mobile and relocatable targets and will “begin looking at automatic target recognition as a component of the capability,” Leaf said. Plans call for fielding this capability by 2009. Officials emphasize that all schedules are tentative and that new SDB capabilities will be added to the program when it is cost-effective to do so.

In a proposed Phase 3, the SDB will acquire loiter, wide area search, and automatic target location and recognition in its kit. This will mark an evolution of SDB from a conventional bomb to something more like a loitering attack missile. The proposed third phase will involve the addition of an “autonomous search and attack” capability, said Greg Jenkins, chief of Air Armament Center’s advanced concepts team.

Little, who is also program manager for the stealthy, Air Force-led Joint Air-to-Surface Standoff Missile, said that seeker development will likely begin around 2006, when the needed technology is more developed and affordable.

The service is currently drafting formal standards for an operational requirements document, said Maj. Ben Quintana, an Air Force officer who led the miniaturized munitions capability Analysis of Alternatives for ACC at Langley AFB, Va. Quintana said industry groups are now preparing proposals. Little added that Lockheed Martin, Boeing, and Raytheon are expected to compete for the developmental contracts, with a Request for Proposals coming this summer.

The RFP will be for the program’s early development phase, officials say. The service will select the two most promising contractor proposals for the first phase, later narrowing down to a single contractor for subsequent production phases.

Little said the warhead size could be around 150 pounds, considerably smaller than the 1,000-pound Joint Direct Attack Munition currently seen as the standard in low-cost precision attack. Unclassified program goals call for a range of up to 35 miles and accuracy of 13 meters, with a 250-pound warhead seen as the probable size, officials say.


“Small Diameter Bomb will reduce the time it takes … to service a target set, because you get more bang per sortie,” Leaf said, adding “it will significantly reduce both the time required to achieve [commander in chief] objectives and delivery platform attrition,” through the bomb’s standoff-range capability. “It was a pretty stunning Analysis of Alternatives,” he added.

The analysis validated the small bomb concept by demonstrating that a small smart bomb can significantly increase combat capability compared to other weapons, including the 500-pound JDAM, Quintana said. The 500-pound JDAM was the “baseline capability” other proposals were evaluated against. The analysis “was a big project that looked at all fighters and bombers,” he added.

Leaf said the shift to a smaller size will be effective against many targets and will simplify targeting and logistics. “It takes care of business without having [a] broad area [that] it destroys,” he noted. “It’s a smaller weapon, so it will take up less space. There’s a big difference between that size weapon and a 2,000-pounder, in terms of explosive safety. … When I was at Aviano [AB, Italy] during the air war over Serbia, one of our very big concerns was very tight, cramped areas. We had a lot of explosives pre-positioned and hung on airplanes, and there’s some risk to that. You reduce that risk and you reduce… the logistics requirement” by moving away from reliance on 1,000-pound weapons, he said.

The new small bomb, despite its potential, doesn’t mean elimination of big bombs. “The key is the effects,” Leaf said-whether or not a small bomb can destroy the target. There are certainly cases where a larger bomb will still be required, he said.

SDB would not be appropriate if “you can’t achieve the necessary precision because of the nature of the target, and you need the greater explosive weight” that larger bombs deliver. Hardened targets, reinforced facilities, and large-area targets are other examples where larger bombs will continue to be weapons of choice.

“In real general war, there are times when the brute force of a big explosion has value, too, not necessarily limited to its destructive power. War is a human endeavor,” Leaf noted. “In a real tough, big fight, sometimes tidiness isn’t the objective. You are trying to compel the enemy [with] brutishness beyond just the ability to service a target.”

Adam J. Hebert is the senior correspondent for, an Internet defense information site, and contributing editor for “Inside the Air Force,” a Washington, D.C.-based defense newsletter. His most recent article for Air Force Magazine, “Why the Allies Can’t Keep Up,” appeared in the March 2001 issue.