In the last decade, the U.S. has purchased about ten million bullet proof ceramic composite plates (SAPI, for Small Arms Protective Inserts) for the protective vests troops wear. Why so many? It's because the plates are bullet-proof, but only once or twice. The plates will stop high-powered rifle bullets, but this weakens the plates, often causing them to crack or chip. So every time a plate is hit, it is discarded and a new one slipped into the vest. The brittleness of these plates means they can be cracked if dropped, or otherwise allowed to hit a hard surface. It’s an odd characteristic for plates that will stop high-powered 7.62mm bullets, but it works. The downside is that the plates are not particularly durable, and wear out quickly on the battlefield.
Another reason for so many plates purchased is the development of new model plates, while many of the older ones were still available. Thus, for four years now, the U.S. Army and Marines have been replacing existing SAPI ceramic bulletproof plates, with thicker, and heavier (by about 37 percent) ESAPI plates. The new ESAPI provides better protection from any kind of high powered bullet.
The basic "Level 3" SAPI plates are 25.4x305cm (10x12 inches) and weigh 2.1 kg (4.6 pounds) each. For greater protection, the older Level 4 SAPI plates, weighing about 2.9 kg (6.4 pounds) each, could stop some types of armor piercing bullets, but so can the lighter ESAPI (which are more expensive, at $450 a plate, down from $600 two years ago).
Weight is a big issue for the infantry, especially when operating in tropical climates. Troops do all sorts of things to save weight, and using the less bullet-proof SAPI plates was just one of them. Thus the SAPI plates remained popular on the battlefield, even as the new ESAPI plates arrived. Many of the SAPI plates were given to combat support troops, who rarely got shot at, but wanted some protection for those occasions. These troops, in contrast, didn't mind the extra weight and preferred ESAPI.
All these plates are made of boron carbide ceramic with a spectra shield backing. This combination causes bullets to fragment and slow down before getting through the plate. Occasionally, some fragments will get through, but these are stopped by the layers of Kevlar that make up the flak jackets. The ceramic plates require a manufacturing process that uses, and produces, a lot of toxic chemicals. As a result of this, much of the production has moved to China.
The success of the plates, and the frequent attacks on U.S. troops in Iraq and Afghanistan, led the U.S. Army to try and get enough plates for all troops in the combat zone, not just those in infantry units. This was more of a morale issue than anything else, as non-infantry troops are most frequently exposed to bombs and RPGs. The fragments from these weapons can be stopped by the flak jackets without the plates. But morale is important, so the army hustled to get enough SAPI plates for everyone. The military has spent over $10 billion on various types of SAPI, ESAPI and XSAPI plates in the last decade.
Sometimes the effort to build "better" (for generals and politicians, not troops) plates backfires. Such was the case when the army bought 120,000 XSAPI bulletproof plates two years ago. These plates were specially designed to protect against a type of bullet that the army would not reveal. The XSAPI plates weigh about ten percent more than the ESAPI plates, but are constructed of the same materials. It’s believed the XSAPI provides protection against some kind of armor piercing bullets. These were long rumored to be used by Iraqi and Afghan terrorists. But, in fact, these bullets were never encountered. So, the theory goes, the XSAPI plates were never issued, and are held in reserve, just in case. Troops have noted that they rarely encountered enemy troops using armor piercing bullets. Thus the older SAPI plates were preferred, simply because they saved a lot of weight. In fact, no one could actually produce any firm evidence of any kind of armor piercing bullets, but combat troops learned every day that weight is real, and it kills.
