The U.S. Army is carrying out an aggressive development program to produce a new, lightweight composite armor for its next generation tank. This vehicle, part of the FCS (Future Combat System) series of vehicles, will weigh under 30 tons. The current U.S. tank, the M-1, weighs 70 tons. Composite armor was invented in Britain during the 1980s. The British developers had found that layers of different metals and ceramics made the armor lighter, and more resistant to penetration by solid shot or HEAT shells. The U.S. added a layer of depleted uranium to its composite armor, and produced the most penetration resistant tank armor ever.

Now U.S. Army developers are betting that they can come up with breakthroughs in composite armor design that will produce protection equal to what the M-1 now has, but at less than half the weight. The army developers are doing it by trial and error, making some progress most months. It's still unknown if the new lightweight armor will be there in time for the new tank's debut date in 2015.

The army developers are encouraged by some of the work done during the current war, especially accidental discoveries. For example, troops in Iraq noticed that although EFPs (Explosively Formed Projectiles) go through metal armor, often glass laminate armor (aka glass ballistic laminate armor) will stop them. Troops reported that the EFPs would not go through the bullet proof windows, which are made of glass laminate. However, the glass laminate only works once. When an EFP strikes the glass, the glass "spiderwebs" (shatters laterally and vertically) but it stops the penetrator. Of course it only needs to work once. Troops lives are saved and the stuff can be replaced. At least one unit is experimented with mounting field improvised brackets outside the doors of vehicles to hold the three-inch thick glass laminate armor.

Apparently the glass laminate armor destabilized the explosively forged projectile penetrator and redirected its kinetic energy laterally along the glass armor laminations. This is the principle behind the M-1 tanks chobham armor (a sandwich of metal and ceramic laminates). The ceramic armor is held in a metal armor matrix. As heavy metal "long rod" penetrator or high explosive shaped charge debris streams enter these armor matrixes, they are destabilized. The kinetic energy is diverted laterally from the initial penetrator direction of attack as the ceramics shatter. A plus here is that the Chobham ceramics are jostled by the penetrator's or shaped charge stream's passage and keep abrading until the attack runs out of energy.

Glass ballistic laminate is expensive. One windshield costs several thousand dollars. The lamination process has a high scrap rate. It takes several tries to create one good, large piece of the material. The silica/polycarbonate plastic sandwich is hard to heat evenly and if it is not perfectly shaped a "void" will appear in during the curing process. This creates visibility issues, and troops need to be able to see through the glass. But it was an interesting discovery, and there were others as well.

These are the kinds of problems army armor developers have to solve if they are going to create a "30 ton M-1." In addition to the lightweight composites, the army is also working on improved ERA (Explosive Reactive Armor.) Invented by the Israelis in the 1970s, ERA consists of explosives packaged between layers of sheet metal. When the hot gas jet produced by a shaped charge (of an RPG or missile warhead) hits the ERA explosives, the gas jet is disrupted and rendered harmless by the ERA explosion. Many American M-2 and AAV-7 armored vehicles in Iraq are protected by ERA kits (which cost over $100,000 each). A Stryker ERA kit costs nearly $300,000 per vehicle, and adds 3.5 tons of weight (compared to 2.5 tons for the current slat armor it will replace.)

There are two shortcomings with ERA. One is that, once a section of it explodes, that section is obviously, no longer protecting the vehicle. Also, it takes 50 or more pieces of ERA to protect a vehicle. The other problem is that, when ERA explodes, it expels some metal fragments that can injure nearby friendly troops. There are solutions. CLARA ERA uses several layers of composites (non-metal material) and explosives which, when they disrupt a shaped charge gas jet, only create lightweight chaff. CLARA is much lighter than standard ERA, weighing about an ounce per square foot, versus several pounds per square foot for standard ERA. There is also SLERA (Self Limiting ERA), which uses smaller amounts of explosives to disrupt the gas jet, and less destruction to the section of ERA itself. This also results in lighter ERA. Both these types of ERA are more expensive, and lack much combat experience.

Finally, there is APS (Active Protection System.) These usually consist of a radar to detect incoming missiles, and small rockets to rush out and disable the incoming thre