Armor: EFP Proofing

December31, 2008: The U.S. Marine Corps is buying additional armor kits for 196 of its Cougar MRAPs (Mine Resistant Ambush Protected) vehicles. This will protect the vehicles from explosively formed penetrator (EFP) weapons. Last year, about five percent of the Coalition combat deaths in Iraq, and about eleven percent of those killed by roadside bombs, were because of EFPs. This year, EFPs have become much less of a problem, partly because fewer have been used, and partly because there are more vehicles out there with the additional armor..

The EFP is nasty because it can penetrate the armor on just about anything but an M-1 tank. An EFP is a precision weapon, a cylindrical device, that is often described as similar to a coffee can. But the cylinder metal must be thicker. You fill about 60 percent of the "coffee can" with explosives (C4, also known as plastique, will do). Then you insert a detonator on the closed end of the "coffee can" and a concave copper plug that is pushed into the plastic explosive. The tricky part here is that the depth of the concave copper part, and the thickness of the copper, have to be just right. It requires someone expert at math and the chemistry of explosives to make those calculations. When you  make a mould for casting the copper plug,  you must make sure you get the thickness just right. The more precisely the copper plug is made, and the EFP assembled, the more armor the device will penetrate, and the more damage it will do inside the target vehicle.

The additional side armor for defeating EFPs consists of 18mm plates constructed of several layers of different materials. This material, which costs about \$2,000 per square foot, breaks up the EFP molten copper "warhead" that an EFP produces to slice through conventional armor. For the six wheel Cougar, the EFP armor kit weighs 2.5 tons, and costs \$152,000. By adding this side armor to an MRAP, most EFPs can be defeated, usually with fatal consequences to the attacker, who is quickly fired on by the troops in the MRAP, and other vehicles in the convoy. Last year, about 300 MRAPs were equipped with this side armor. These up-armored models are used in areas most likely to encounter EFP attacks.

Cougar is a 12-19 ton truck that is hardened to survive bombs and mines. The Cougar comes in two versions. The four wheel one can carry ten passengers, the six wheel one can carry 16. All but four of the 196 EFP armor kits are for the six wheel version. The Cougar uses a capsule design to protect the passengers and key vehicle components mines and roadside bombs. The trucks cost about \$730,000 each, fully equipped. The Cougars have proved very popular with the troops, but the additional weight makes the vehicle difficult to handle on many dirt roads in Afghanistan and Iraq. The road shoulders collapse under weight, and the high center of gravity typical of MRAPs can lead to a roll over.

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