This Strafor article by Scott Stewart discusses a video from Syria that showed an attack by militants against an army bus.
The video seems to show that the IED was a explosively formed penetrator (EFP), which are more sophisticated than normal IED in that they focus their blast in a smaller area and are more effective against armor.
After a discussion of the fabrication of EFPs, Scott turns to the possibility of they, or at least the technology to make them, being provided by outside sources.
The beginning of the article is excerpted below, with a link to the full article at the end of the excerpt.
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Are Syria's Rebels Getting Foreign Support?
By Scott Stewart, June 21, 2012
A video recently posted to the Internet depicting an improvised explosive device (IED) attack in Syria has garnered a great deal of attention. A Syrian militant group called the Hawks Brigade of the Levant claimed the attack, which targeted a Syrian government armored troop bus as it traveled along a road near a rebel stronghold in the Idlib governorate. According to the group, the attack depicted in the video employed a type of IED called an explosively formed penetrator (EFP). Though the video was shot from a fairly long distance away, it does appear that the IED punched a substantial and focused hole through the armored bus -- precisely the type of effect that would be expected if an EFP were employed against such a target.
EFPs are a logical tool for militants to use against superior government forces that are heavily dependent upon armor. EFPs pose a significant threat to armored vehicles, which the Syrian military has utilized extensively, and quite effectively, in its campaign against Syrian rebel groups.
Studying the IED technology employed by a militant group is an important way to determine the group's logistics situation and trajectory. It can also be a way to discern if a group is receiving outside training and logistical assistance.
Explosively Formed Penetrators
An explosively formed penetrator, sometimes called an explosively formed projectile, is a simple device composed of a case, a liner and explosive filler. EFPs have been part of many countries' military inventories for years. The U.S. Army, for example, added the M2 Selectable Lightweight Attack Munition (aptly named the SLAM) to its inventory in 1990. Improvised EFP devices can also be constructed by non-state actors; they were widely used to target U.S. military vehicles in Iraq.
The employment of an EFP device in the field also requires a detonator and a firing chain to initiate the detonator. The firing chain can vary widely, from a hardwired command-detonated system to an improvised victim-actuated system that is triggered inadvertently by the target and involves modifying things like the infrared safety beam from a garage door opener.
The case of an improvised EFP is often constructed from a short section of well-casing pipe with a steel plate welded to one end. A small hole is drilled in the plate to allow a blasting cap to be inserted. The pipe is then filled with high explosive, and a metal liner -- most often made of copper -- is affixed over the open end of the pipe.
EFPs utilize the same general principle as a shaped charge. In a traditional shaped-charge munition like the warhead on an anti-tank rocket, a thin metal cone is used to achieve a focusing effect. When crushed, the concave metal cone in the warhead becomes a molten, high-velocity projectile that, with a jet of super-heated gas from the explosive, penetrates the armor. However, in order for a shaped charge to work most effectively and achieve maximum penetration it must detonate at a precise, relatively short distance from its target. In a munition like a rocket-propelled grenade, an empty space between the nose of the warhead and the copper cone generally provides the required standoff distance.
The EFP munition is somewhat like a traditional shaped charge, but it incorporates a metal liner with less of an angle. So instead of forming a cone, the liner is more of a concave lens or dish shape. The EFP also uses a heavier liner that is formed into a slug or "penetrator" when the device is detonated. The penetrator is then propelled at the target at an extremely high velocity. The difference in the shape and weight of the liner allows the EFP to be deployed from a greater distance than a traditional shaped charge.
Because the components required to construct EFPs are simple, such devices can be fabricated inexpensively and out of readily available materials. Well-casing pipe and steel plate, for example, are widely available in almost any region of the world. Moreover, making the EFP casing from these elements requires little skill and simple machinery, such as a welder, a grinder and a drill.
The copper liner is the sophisticated part of the device, requiring a bit more precision in its fabrication. If the liner is not formed in a precise manner, the devices will tend to spit copper shrapnel rather than create a truly effective penetrator. However, once the proper shape of the liner is determined, either by copying the shape of the liner in a professionally designed EFP device or by trial and testing, the liners can be fabricated somewhat easily using a form and a hydraulic press.
Read more: Are Syria's Rebels Getting Foreign Support? | Stratfor