It was very sad to hear about the recent downing of the Chinook helicopter in Afghanistan that killed 38 soldiers. Eastern Afghanistan has steep mountain ranges, providing shelter for militants with rocket-propelled grenade launchers creating a dangerous area for military aircraft and personnel. Large, slow-moving air transports like the CH-47 Chinook are particularly vulnerable, so the military should not be surprised that one was shot down especially if it is not equipped with countermeasures as it is a relatively defenseless aircraft.
The two greatest dangers faced in asymmetric warfare are improvised explosive devices (IED) and rock propelled grenades (RPG) as they are easy to obtain and widely used by insurgents. Large funding has gone into IED defeat systems in the US, such the Warlock and JCREW programs, with thousands of systems being fielded. These are RF based systems to jam wireless frequencies that remotely detonate the IEDs. The systems have been relatively effective but there are other ways to detonate IEDs (wires, pressure plates, etc.) so they are not a total solution to defeat them. However, there seems to be much less emphasis put on defeating RPGs as there are only a few systems available today.
Most solutions are deployed on land vehicles which have cages or nets around them that are designed to defeat RPGs but these would not be appropriate for airborne vehicles (photo courtesy of Polish military). There are a couple of active RPG defeat systems that have been developed for vehicles that use RF technology. Rafael Advanced Defense Systems and Israel Aircraft Industries' Elta Group developed an active protection system called Trophy. Trophy intercepts and destroys incoming missiles and rockets with a shotgun-like blast by using radar sensors to track the incoming RPGs. The system includes the Elta EL/M-2133 F/G-band fire-control radar with four flat-panel antennas mounted on the vehicle, that has a 360-degree field of view. A computer uses the signal from the incoming weapon and calculates an approach vector. The system then calculates the optimal time and angle to fire the neutralizers. The launchers fire the neutralizing agents, which are usually small metal pellets (like buckshot).
A few years ago it was reported that there was resistance to incorporating Trophy into the US Army. The US DoD had contracted with Raytheon to develop a similar system, Quick Kill, which at the time was several years behind Trophy in development so there were rumors they wanted their own system instead of the Trophy. Later, in February 2011, Rafael announced that the Trophy system completed a successful evaluation in the US. This system is primarily intended to be used on ground vehicles so these systems probably need to be adapted to be used on airborne vehicles.
Another system that is a non-lethal RPG defeat concept is the RPGNet from Qinetiq US that uses a net shaped "trap" made of super-high strength ballistic fiber, developed under a joint ONR/DARPA program. The net intercepts the flight trajectory at a safe distance from the vehicle and defeats the RPG by crushing its nose, rendering the fuse inoperable. This prevents the high-order blast effect by preventing the formation of the shaped charge plasma jet. The system is in development by Foster Miller from program for the Office of Naval Research (ONR).
Several US companies are working on systems to defeat RPGs but they seem behind several other countries like Israel and the UK. General Dynamics has developed the ShotScreen™ RPG Defeat System which is an active protection system that can be mounted on new or retrofitted on a variety of vehicles including helicopters. The system releases a wave of small diameter, low velocity non-lethal pellets from several non-slewing locations to defeat multiple anti-tank type RPGs. It provides 360° horizontal protection with variable inclination coverage and an option for full hemispherical coverage. As mentioned previously, Raytheon has also worked on active protection systems.
Asymmetric warfare presents different challenges than the military is used to dealing with over the years so priorities need to be assessed and new systems deployed quickly to meet these new challenges. Airborne vehicles operating in insurgent areas need protection/countermeasures such as RPG defeat systems which should be more of a priority for the military on vehicles performing critical missions such as the Chinook that was shot down.