The armed services, as well as private industry concerns, both in the U.S. and overseas, have devised and continue to develop defenses that protect vehicles from the worst of an RPG or similar attack. These defensive systems can be broadly divided into two categories. Passive defenses, such as netting or bar armor, equip a vehicle with material designed to absorb the force and blunt the trauma associated with an RPG hit. Active defenses are those mounted on vehicles that detect, classify and track incoming threats before launching a countermeasure which either blocks or diverts an RPG, or disables it in such a way as to prevent it from penetrating the vehicle’s armor.

The Defense Advanced Research Projects Agency (DARPA) began working on a vehicle protection system five years ago, in response to developments in the war in Iraq. “Our program was designed around protecting light tactical vehicles,” said Karen Wood, a program manager in DARPA’s strategic technology office. “That is where we were suffering the heaviest damage in Iraq—from bullets, RPGs, direct-fired mortars and anti-tank guided missiles, and we wanted to see what we could do to help with their survivability.”

The DARPA program, dubbed Crosshairs, contains a number of components, including an active protection system. DARPA tested a number of passive protection systems before deciding to integrate the active system, known as Iron Curtain.

The Office of Naval Research is also sponsoring science and technology research and development on vehicle protection systems for eventual transition to the Navy and Marine Corps. “Within the confines of what we can do against RPGs, we have invested in non-lethal approaches to protect Marines in the field and naval forces,” said Rodney Peterson, an ONR program manager. “The fact that Marines and troops are outside of their vehicles much of the time means we need to have a non-lethal protection mechanism to incapacitate an incoming threat without endangering troops outside the vehicle.”

One example of a passive defense for tactical vehicles was developed in the United Kingdom by AmSafe. Known as Tarian, the Welsh word for shield, AmSafe’s is a textile-based system specifically designed to defeat RPGs. The company began development of Tarian in 2005 in conjunction with a U.K. Ministry of Defence laboratory. Testing took place last year.

“The product is based on the application of lightweight textiles to provide armor,” said Neal McKeever, the company’s director and general manager for defense. “Tarian can replace traditional steel or aluminum bars or slat armor. We are unable to disclose details of how Tarian works because of a secrecy order we have with the MOD, but it does work in a similar fashion to steel or aluminum.”

Textile-based solutions such as Tarian, as well as steel and aluminum bar protection, are mounted away from a vehicle’s surface so that the tip of a flying RPG warhead hits the outer protective layer first. This triggers the RPG to form its plasma jet prematurely, dissipating much of its focus and energy by the time the weapon strikes the vehicle’s armor plate, and lacking the force to pierce it.

The key advantage that Tarian offers over its metallic cohorts is a 50 percent weight savings off aluminum and 85 percent off steel bar armor. “One of the specific opportunities that the British army sees with the weight savings is that more equipment, ammunition and supplies can be added to the vehicle,” said McKeever.

Tarian is being evaluated on the U.K.’s heavy equipment transport (HET) vehicle and on the Spartan armored reconnaissance vehicle. In the U.S., DARPA is also testing Tarian. McKeever believes that once Tarian passes its tests on the HET, “there will be keen interest to transition the product to other vehicle types.”

Active RPG protection systems include the ASPRO (armored shield protection) system, also known as Trophy, marketed by Israel’s Rafael Advanced Defense Systems. The systems are designed to enhance the survivability of tracked and wheeled armored tactical vehicles against a variety of battlefield threats.

Trophy defeats incoming threats with three phases of operation: threat detection, threat tracking, and finally, activation of the hard-kill mechanism that neutralizes the threat using a countermeasure before it impacts the vehicle.

The threat detection and warning subsystem consists of several sensors, including search radar with four flat-panel antennas, located around the protected vehicle. The neutralization process takes place only if the threat is about to hit the platform.

Trophy has already been retrofitted on some of the Israel Defense Force’s existing Merkava Mk 4s. All Merkavas now coming off production lines are being outfitted with Trophy, according to Didi Ben-Yoash, Rafael’s business development manager.

“The system detects, tracks and classifies threats by radar,” explained Ben- Yoash, “and then destroys the threat with a countermeasure. Trophy protects against a wide range of threats, including all known anti-tank rockets and anti-tank missiles. The system provides full performance against shortrange threats, in close and urban terrain, and under all weather conditions. It can engage several threats from each direction arriving simultaneously.”

The countermeasure is based on a technology known as multiple explosive form penetrators (MEFP). “MEFP is a way to create a very fast hit directly at the incoming threat,” said Ben-Yoash. MEFP technology was developed in the 1980s to provide a warhead that could produce many penetrators to attack light materiel targets.

It took Rafael around 15 years to develop Trophy, said Ben-Yoash. The system was declared operational in August 2009. Published reports have indicated that Rafael has exported Trophy to several military organizations in countries outside of Israel, but Ben-Yoash was unwilling to comment on any international sales.

The DARPA Iron Curtain is being developed by Artis LLC, a McLean, Va.,-based company under contract to DARPA. Iron Curtain consists of four major component groups.

“When a tactical vehicle is rolling down the road, the system is not in an armed state for safety reasons,” explained Keith Brendley, the president of Artis. “An incoming RPG will be detected by a C-band radar system, which then communicates the threat to a fire control system which then decides whether to put system into an armed state.”

Once Iron Curtain switches to an armed state, the sensing is handed off to a series of optical sensors that are distributed around the vehicle. “The optical sensor looks at the threat in detail, and an automatic target recognition system associated with the optical sensor determines what the incoming threat is, right down to the type of RPG,” said Brendley. “The optical sensor profiles and classifies the threat to select the proper aim point and determine which countermeasure to fire.”

Once the system determines that the RPG is on course to hit the vehicle, a countermunition mounted on a vehicle roof rack is activated. “The counter-munition acts straight down so that there is no collateral damage,” said Brendley. “One of the big features of the system is its accuracy. We are able to hit precisely the part of the threat we are aiming at.”

When the RPG is within inches of the protected vehicle, the countermeasure is deployed, disabling the weapon without detonating it and causing the disabled RPG to bounce off the vehicle side. It may cause some damage to the vehicle, Brendley noted, but it will not be able to penetrate the vehicle armor. “You still need some armor, but not much,” he said.

Iron Curtain currently defeats all known RPG threats and is moving toward the ability to defeat more challenging threats such as anti-tank guided missiles. “Iron Curtain’s ability to profile and classify targets enables it to efficiently address new and emerging threats, usually with nothing more than a software change,” said Brendley. “This flexibility prevents Iron Curtain from becoming obsolete.”

Iron Curtain is part of a larger DARPA vehicle protection program called Crosshairs, which was devised to develop a number of capabilities. First, is a detection tracking and shooter localization capability. The next is a capability that facilitates a response decision. The third capability involves controls and displays to designate targets and improve situational awareness.

“The fourth capability is networking,” said Wood. “We use EPLRS [enhanced position location reporting system] compatible radios to network to surrounding vehicles so that they are aware of the shooter and the threat. The fifth capability is an active protection system. Out of that effort finally came Iron Curtain.”

Before deciding on Iron Curtain, DARPA considered other alternatives for Crosshairs, including passive defense systems such as metal mesh anti-RPG netting and bar armor. “We developed the sensor system and other capabilities in parallel,” said Wood. “We are now in the process of taking the first four Crosshairs capabilities and are integrating the survivability piece, which turns out to be Iron Curtain.”

DARPA is currently in the final phase of preparing the system for testing on HMMWVs and mine resistant ambush protected (MRAP) vehicles. “We expect that the MRAP program office will look at Crosshairs as a potential counter-RPG solution,” said Wood. “There is currently an urgent needs statement for a counter-RPG system in Afghanistan that this can address.”

Once testing is done, Brendley believes that Iron Curtain can be fielded fairly rapidly. “We anticipate being designated as a UMR [urgent material release],” he said. “That is the assumption that DARPA has instructed us to work under.” Brendley anticipates an initial deployment of several dozen systems, “followed by a much larger number.”

The Office of Naval Research has demonstrated a system called Shotscreen, developed by Mechanical Solutions Inc. of Whippany, N.J. Shotscreen, like Crosshairs and Iron Curtain, uses sensors to detect an incoming threat and a countermeasure to defeat it. One difference between Iron Curtain and Shotscreen is that Shotscreen defeats the threat at a 20 to 30 feet standoff from the protected vehicle.

Peterson said ONR has been collaborating with DARPA and the U.S. Army on this project and noted that it may be appropriate to develop more than one anti-RPG active protection system. “There may be a number of different paths to defeating an RPG or a threat of similar magnitude,” he said. “Different kinds of packages may be heavier or lighter, more or less complex, or may involve mechanisms that users may prefer or not prefer.”

Shotscreen started as a Small Business Innovation Research (SBIR) project in 2009 and is currently at the end of the first year of a two-year commercialization phase. “Within one year we believe we will be acquiring a prototype of the system and conducting a demonstration for the Marine Corps,” said Peterson.

After that, it will be up to program managers in the Army and Marine Corps to decide whether they wish to proceed with procurement and acquisition activities with Shotscreen. “At that point, there may be further research and development to adapt Shotscreen to specific systems before it is eventually acquired and fielded by one or more of the armed services,” said Peterson.

An active RPG defense that combines the attributes of a live countermeasure and a barrier defense is being developed by Control Products Inc., an engineering company based in East Hanover, N.J. The company is working on an RPG barrier that is launched from the vehicle to intercept a threat several yards from the vehicle.

”We have developed a fairly robust barrier in the shape of a parachute that is towed by a single solid fuel rocket and which achieves the objective of creating a barrier away from the host vehicle,” said CPI’s Rich Glasson. This minimizes the threat of fratricide, he noted. CPI’s system does not include a threat detection component. “Our system is the responding component,” said Glasson. “We receive the threat vector and launch the countermeasure.”

Once the countermeasure is launched, the parachute-like barrier is unfurled, and it is that device which deflects the RPG off of its original course.

Glasson contended that actually catching and stopping an RPG is exceedingly difficult because of the velocity and mass of the weapon. But testing on CPI’s barrier system, which includes a counter-munition similar to that of an RPG, has shown that it is possible to mitigate the effects of an RPG attack by disrupting the weapon’s flight path, by defusing the munition and causing it to blow itself up, or to deform the weapon and prevent it from forming the plasma jet necessary to penetrate steel armor when it explodes.

“Our barrier seeks to deflect, deform and defuse the RPG before striking its intended target, and not to catch and stop it,” said Glasson. “One of the advantages of our system is that it covers a wider area. We’re not trying to hit a bullet with a bullet, and we don’t have to precisely strike a fast moving target. We just have to put the barrier out there.”