During World War II, waves of Allied aircraft dropped thousands of bombs on German cities, military installations, railroads, and industrial facilities. Where a given bomb might hit was as much luck as skill – and even massive bombing raids often failed to destroy their actual target, despite devastating everything around it.

Half a century later, a single aircraft carrying “smart” bombs with global positioning system (GPS) guidance could do more militarily significant damage to the enemy than an entire fleet of World War II aircraft on “carpet-bombing” missions. And unlike the German V-2 rockets that terrorized London, long-range cruise missiles fired from ships in the Persian Gulf were able to seek out and hit a specific building in the middle of Baghdad.

A decade later, the second Gulf War saw another leap in precision-guided munitions (PGMs), by then sufficiently accurate to hit a specific window in a building hundreds of miles away, or, when carried by an unmanned aerial vehicle (UAV), fly over an area of interest until a predetermined target or target of opportunity was located, then take it out on the spot, following commands from a human pilot half a world away.

The targeting radars used by World War II pilots, along with ship-based big guns and submarine torpedoes, brought a new concept of weapon accuracy to military operations at the time, especially at long range. Each decade that followed brought weapon effects closer and closer to their intended targets, reducing collateral damage and the number of bombs, missiles, and platforms required.

But by the 1990s, the combination of ever-faster, smaller, and more capable computers with the near-pinpoint accuracy of GPS guidance and navigation systems and more powerful, reliable conventional explosives changed mere accuracy into precision. By the turn of the century, PGMs had become a staple in U.S. and allied military arsenals.

As weapons at all levels became more and more accurate over longer distances and in increasingly harsh environmental conditions, precision guidance evolved one more step, becoming precision strike. And the targets against which precision strike could be applied became smaller and more specific, advancing from hitting a specific room in a building to, ultimately, a specific individual in that room.

While the latter has always been the hallmark of the military sniper, they, too, have benefited from improved weaponry and technology – to the point where a Canadian sniper in Afghanistan recorded the longest kill shot in history, hitting a Taliban fighter from a mile-and-a-half away.

The accuracy evolution also affected some of the oldest weapons on the battlefield, turning cannon and mortars from area to precision weapons. Currently in development for possible fielding in the new decade is a combat boot chip that will guide a dismounted warfighter to his target without the use of GPS. Combined with rifles firing guided bullets, that could make the foot soldier a precision strike weapon within the next five to 10 years.

The individual soldier who employs these new types of precision strike weapons will not need a graduate degree in engineering to do so, but will be far more highly trained and knowledgeable than previous generations. Old skills such as “Kentucky windage” will remain, but the future language of precision guidance/navigation and strike also will include atom interferometry, gravity gradiometers, chip-scale atomic clocks (CSACs), nano-g, nano-inertial navigation system (INS), Zero velocity UPdaTing (ZUPTing), electrostatic levitation, micro-electro-mechanical systems (MEMS), micromechanical resonators, cybernet neutralization, dynamically tailorable in-flight munitions, high-power solid state lasers (SSLs), neodymium yttrium aluminum garnet (Nd:YAG), short wave infrared (SWIR), microbolometer long-wave detector, scalable warheads, and GPS M-Code.

A few old terms, however, have, if anything, increasing importance: cost, interoperability, logistics tail, reliability, combat rugged, ease of use. Part of addressing those will involve an increased capability to take old weapons already present in large numbers and enhance them to precision – or at least near-precision – grade, in the field or depot, with little training and no new tools.

The Defense Advanced Research Projects Agency (DARPA), as usual, is at the forefront of new guidance and navigation technologies. One such program in DARPA’s Defense Science Office is Precision Inertial Navigation Systems (PINS), under the management of USAF Lt. Col. Jay Lowell. PINS is an effort to address the vulnerabilities of GPS navigation – jamming, spoofing, blind spots, etc. – by using ultra-cold atom interferometers to reduce the positional accuracy drift of INS by several magnitudes, giving it near-GPS accuracy.

Such a system could be used as a backup in case of GPS denial or as an alternative to GPS on some platforms. Lowell believes it not only is the core technology for future improvements in high-end INS, but offers real promise as a key element in future global strike.

“The goal has been to mature this from a scientific investigation done in university labs into devices capable of stand-alone operations on moving platforms to produce navigation solutions,” he said, adding it can improve INS “drift” by a factor of 70 – typically 1 mile per hour for a stationary aircraft-size box to only tens of meters an hour with PINS. “That’s how much performance scaling this new technology has compared to existing inertial technologies.”

Because it could be used in place of GPS, the original goal was to develop an underwater capability that would enable submarines to maintain positional and navigation accuracies without surfacing as often to acquire satellite signals. However, DARPA believes atom interferometry will be an enabling technology for improved navigation for aircraft, missiles, and even satellites as well, using atomic sensors many times more sensitive to inertial forces than existing navigation technologies.

The current challenge is improving sensor bandwidth and using miniaturization and integrated subsystems to enable operations with a 10 g input that would be applicable to aircraft and missile navigation, specifically hypersonic missiles.

“That is a necessary condition and why the 10 g number was chosen. And at that point, we can look at specific tests beyond 10 g inputs for them to have good confidence the technology can provide navigation solutions for hypersonic vehicles,” Lowell said. “So I’ve been talking to people working on hypersonic munitions and trying to give them the insights they need to see the applicability of the technology to their problem.”

Demonstrations of the individual components of such an advanced INS already have achieved world-class performance, he said. As a result, airborne tests in the next three or four years offer the possibility of a routinely fieldable application by 2016.

“We have vacuum systems, lasers, frequency stabilization to go with the lasers, and the process of cooling and trapping the atoms, all of which lay out into various subsystems that have to operate and function appropriately,” Lowell said. “The accelerometer bias is below 1 nano-g, compared to about 1 micro-g in most systems. This system is trying to determine gravity gradients over 1 meter or less; it can detect the gravity field of a human being walking up to the instrument.

“Our 24-hour gyroscope bias is below 10 microdegrees per hour, where most aircraft navigation systems operate in the 10 millidegree per hour range. In fact, a navigation grade gyroscope is considered between 1 and 10 millidegree bias, so we are 100 to 1,000 degrees better in the lab and we hope to maintain much of that performance as we go forward and shrink this system down to reach our 70 times capability in the same size range.”

While its intended 10 g operational environment was specifically chosen to ensure the technology will be applicable to hypersonic vehicles and munitions, whether that happens depends on Air Force decisions yet to be made.

“It’s my sense they are still forming the requirements for what the navigation system has to do on those vehicles, in part because there is no technology that does what they want it to do. This may do that,” Lowell said. “It’s the only thing with sufficient headroom to react; by that, I mean we have not yet come even close to the performance limits of this technology.

“Like any navigation technology, there is a tremendous tradeoff with system size. In the size we’re talking about, we’re actually limited by geophysics – the Earth’s gravitational field fluctuates temporally and spatially in such a way we really don’t need to make the system any better than we’re making it. It’s the first time that can be said about an inertial technology at this size scale.”

PINS also is still considered a major improvement for its original target platform – submarines.

“Underwater munitions are a different breed. All are active, the equivalent of a radar-guided air-to-air missile, which is always an active system. So it isn’t really important for underwater munitions, but very important for underwater platforms, which can only go so long before they get lost or have to come up to figure out where they are,” he said. “We believe PINS will enable those platforms to operate for far longer periods of time without exposing themselves to the surface and the jeopardy of being detected.”

Another DARPA program, managed by Dr. Lyn Beamer in the Information Processing Technology Office (IPTO), is the EXtreme ACcuracy Tasked

Ordnance (EXACTO), formerly known as the Laser Guided Bullet.

According to the unclassified description of this classified program in DARPA’s 2010 budget request, EXACTO will enable sniper teams “to identify and engage targets with heretofore unobtainable range and accuracy against stationary and moving targets under difficult environmental conditions, either day or night … The system uses a combination of a maneuverable bullet and a real-time guidance system to track the target and deliver the projectile to target. Technology development includes the design and integration of aero-actuation controls, power sources and sensors. The components must fit into the limited volume (2 cm to the third power) of a .50-caliber projectile and be designed to withstand a high acceleration environment.”

DARPA expects to transfer EXACTO to the Army by FY 2012 for incorporation with a variety of other technologies, from advanced sighting and optical resolution to fin- and spin-stabilized projectiles. The goal, according to Beamer, is to provide snipers with first-shot resolution to currently uncontrollable environmental factors, target motion, minute differences in rounds, etc., all of which now require a number of calibration shots to “walk” their aim to the target. That both warns the target he is under fire and risks exposing the sniper to counterfire.

“Results to date have been very promising. Great progress has been made on two key technical challenges – the ability to communicate with the bullet in flight and the ability to then change the bullet’s course,” Beamer said. “EXACTO will change the attack geometry profile in that it will allow persecution of targets that cannot currently be engaged because of range, terrain, wind, target motion, or other factors. This will greatly increase the effectiveness of snipers, as their shot accuracy becomes independent of environmental conditions, while also increasing sniper safety by allowing much greater standoff distances.”

EXACTO’s current Phase I development will conclude with a hardware-in-the-loop simulation to evaluate system performance before the building and demonstration of a working prototype in Phase II.

While it is pursuing a number of the most advanced technologies, DARPA is not alone in the development of future PGMs. Within the Army’s Program Executive Office-Ammunition (PEO-Ammo), for example, the Project Manager-Combat Ammunition Systems (PM-CAS) is responsible for a number of current and future developments in precision weapons. So is the Army’s Armament Research and Development Center (ARDEC), where efforts from future evolutions of the Excalibur precision-guided extended range artillery projectile, the Accelerated Precision Mortar Initiative (APMI), and the Very Affordable Precision Projectile are being pursued by the Munitions Engineering Technology Center (METC).

METC Director for Fuze & Precision Technologies Bill Smith said the Army and Marine Corps are being driven to greater precision, both broadly and especially in urban environments, by increasingly restrictive rules of engagement designed to reduce collateral damage – both human non-combatants and structures, such as mosques, schools, and hospitals. That has led to new research into “scalable lethality” – weapons that can be calibrated in the field for a range of non-lethal to lethal effects – as well as improved target location and tracking and smaller, more precise munitions.

“To get us there, we need to reduce cost directly in the component, such as MEMS fuzing and IMU [Inertial Measurement Unit], but also employ emerging technologies, such as direct write electronics, which could be the state of the art in some future manufacturing techniques. Many things you can put into a solution, you can use injection printer technology to write onto a surface, which opens the door for a lot of materials technologies in building electronic components,” he said, adding one goal of APMI is a GPS-guided high-explosive cartridge for the 120 mm mortar.

“Again, we have electronics in terms of GPS receivers, power-conditioning going on inside of the electronics package, a guidance processor, and so on,” noted Pete Burke, PM-CAS’ acting deputy product manager for mortars. “And, just like on the artillery variants, it has to survive gun shock and all the other environmental requirements of any military piece of kit – extreme temperatures, vibrations, transport around the battlefield, being dropped, rain-smoke-dust, and a lengthy storage life inside its canister.”

Many of the changes envisioned for 21st century precision weaponry are not limited to improved navigation or terminal guidance, but also at the ability to redirect, vary levels of lethality, operate in any environment – including GPS-denied – alter the timing or shape of an explosion, and even terminate in flight.

“Looking at different ways to shape warhead response will benefit from a lot of novel techniques being developed by industry. To have several electronic initiators in or around a warhead to do that, you need to precisely control when they go off. Outside technologies we could leverage there might include an advance in the state of the art in fast switches, for example,” Smith said.

Dave Dorman, vice president for Business, Development and Strategy for ATKs’ Advanced Weapons Division, said knowing exactly where a warhead will land, then having the ability to tailor its effects, will provide U.S. forces with both the ability to achieve their missions with a smaller logistics tail and significantly reduce collateral damage.

That is the goal of a new Precision Guidance Kit (PGK) ATK is developing for PM-CAS to replace a NATO standard fuze on existing stockpiled artillery ammunition. Dorman said PGK should be fielded in early 2010 for application to millions of existing 155 mm and 105 mm artillery high-explosive projectiles. With its miniaturized GPS chip, PGK is intended to essentially do for field weapons what the Joint Direct Attack Munition (JDAM) did for conventional “dumb” bombs. With PGK, a 155 mm projectile’s circular error probable (CEP) decreases from 175 meters at a range of 20 kilometers and 273 meters at 30 kilometers to only 50 meters at both ranges.

“PGK is a unique application of technologies, including fixed rather than moveable canards, generating our own power in flight, and some unique design characteristics, so it is more an application of technologies at hand, with gun hardening and miniaturization of the GPS being the primary enabling technologies we have utilized,” Dorman said. “We have to harden those GPS chips so they can survive the pressures and shock of gun launch, which was a technology only recently achieved and demonstrated by our GPS provider.”

The result has been a new capability enabling the use of field artillery in urban combat for the first time under current rules of engagement.

“Both the Army and Navy have expressed a desire to see the capability developed to put precision and scalable effects into the warhead, making it a transformational weapon, but without being a huge investment,” he said. “The further you fire with conventional artillery, the more dispersion you have. And as you get into larger caliber weapons – including the 52-caliber barrel in some European systems that allows greater range – firing conventional artillery becomes almost impractical. So it is an area suppression weapon, at best.

“The new PGK allows the military to use the range that conventional ammunition can fire to with a level of accuracy ensuring they can actually hit something. That avoids collateral damage and reduces logistics, meaning fewer resupply convoys that are susceptible to attack.

“Collateral damage in Afghanistan, in particular, is of huge importance. Commanders are doing everything they can to avoid hitting tribal villages that may be friendly but could quickly become enemy forces if an artillery shell inadvertently hits that village. Conventional artillery, with its inherent dispersion, is problematical, so there have been a lot of situations where commanders would have liked to use these weapons but have had to go instead to more expensive PGMs and precision air-dropped munitions. PGK thus gives them a lot more flexibility,” Dorman said.

“Some enemy forces use reverse slopes of hills and steep mountains. Putting rounds on the side of a mountain with 173-meter dispersion, you might hit unintended targets on the valley floor or top of the mountain instead of the goat trail where the bad guys are operating. By dramatically tightening up the CEP, you can put rounds where they need to be.”

Also on the forefront of future precision strike is the use of directed energy weapons – not as a replacement for “traditional” PGMs, but to enhance the flexibility available to combatant commanders to address rapidly changing circumstances. And some of the technologies going into PGMs also are applicable to lasers.

“The pointing stability of a directed energy weapon is actually a high navigation performance. The pointing stability has to be phenomenal over any appreciable distance to hit what you want to hit. PINS is the technology that gives you the angular stability to do that in absolute space over a wide range,” Lowell said. “The trend in the past 10 years or so will continue – the push to smaller and smaller payloads, taking advantage of precision to tailor the payload effect to the commander’s intent.”

Directed energy weapons are perhaps the ultimate in precision strike. While experiments to date have involved the use of chemical lasers – which tend to be large, expensive, and dependent on dangerous chemicals that need periodic replenishment – the future is likely to rest with solid-state lasers and significantly advanced liquid lasers.

Two major directed energy weapons programs currently under way are the joint High Power Solid State Laser (JHPSSL), funded by the Joint Technology Office and the Army to produce a lab-based 100 kilowatt (kW) technology demonstrator; and the High Energy Liquid Laser Area Defense System (HELLADS), a DARPA-funded program to demonstrate an actual 150 kW laser weapons system. JHPSSL is about midway through a three-year program, while HELLADS is approaching demonstration of a 50 kW unit cell demonstration. That is expected to be followed by a two-year phase to build and demonstrate a full 150 kW capability, then transitioning the technology to the Air Force to test on an airborne platform.

“DARPA’s goal [with HELLADS] was to take the present state of the art and try to make an order of magnitude leap in terms of weight and volume. If you can build and demonstrate a laser of this power to those specifications, it then would be compatible with the kinds of platforms on which you would want to deploy the laser, such as an F-35. That has really been one of the main obstacles previously – they were simply too large and too heavy,” Dr. John Boness, vice president-Directed Energy Weapons at Textron Defense Systems (Wilmington, Mass.), told The Year in Defense.

“The publicly released numbers call for building a system at 5 kilograms per kilowatt – or 750 kilograms – and you’re pushing the limits of technology in almost every area to meet those requirements. You have to miniaturize systems by an order of magnitude, the supports and optical systems require lightweight materials, there are considerations involving pulse power and thermal management. It was viewed as a DARPA-hard engineering challenge when we began, but I think we’re doing very well.”

As happened with UAVs, which rose and fell in military interest for decades before coming into their own thanks to technological advances in the 1990s, lasers have been studied for at least three decades. Until now, however, they were not powerful enough at a size, weight, and logistics requirement to be practical. HELLADS and JHPSSL are strong indicators that this is about to change.

“We would certainly like to see 100 kW prototypes in the field within five years – and I think we are on a development pathway now to put demonstrator/prototype systems, especially for the Army and Air Force, into that time frame. To really put them into the field, in combat, would be the next step, perhaps out in the seven- to 10-year range,” Boness said. “In smaller power ranges, if you can convince the military they have a battlefield utility, they could be available more quickly.”

While all the services are pursuing directed energy, it is not seen as a replacement for the next generations of PGMs, he added, but as a complementary capability, providing combatant commanders with greater flexibility to address whatever circumstance they may encounter. And to achieve true precision, even directed energy weapons will rely on many of the guidance and targeting technologies being developed for current and future PGMs.

The application of cutting-edge technologies to a greater range of weapons also reflects what Lowell terms a kind of “meta-trend in navigation” – extending what had been expensive capabilities reserved for a few high-end systems to a far greater number of smaller, more widely used munitions.

“Before, you could only afford a few applications because the components were custom-made and expensive,” he concluded, “where now they are smaller, cheaper, and can be used on many more things than just big platforms.”