The Germans developed the first modern protective vests during World War I. These weighed about 20 pounds, restricted movement and were mainly used by troops who stayed put a lot (like machine-gunners.) During World War II, the U.S. developed a similar "flak jacket" for bomber crews. While not bullet proof, they did offer protection from exploding German anti-aircraft shells ("flak"), which caused most of the wounds for bomber crews. Again, these jackets were too heavy and bulky for the infantry, although these used layers of the new "synthetic silk", nylon, for added protection. At the end of World War II, the army had developed a 12 pound vest, using aluminum plates and nylon fabric. It was still bulky and restricted movement, but was a lot lighter. During the Korean war, an eight pound protective vest, using layers of nylon and a nylon type material (Doron), was provided starting in 1952. While not bullet proof, it was able to stop two thirds of fragments (which caused 75 percent wounds) and some 20 percent of bullets (which caused 25 percent of wounds). Wound injuries to the torso were also reduced by two thirds. And those fragments and bullets that did penetrated did a third less damage. These T-52 vests cost about $280 (in current dollars). Improved versions of the T-52 were used with success in Vietnam, although these things were very hot in tropical climates. Often troops did not wear them if they knew they would be moving around a lot.
In the early 1970s, Kevlar vests were produced. Kevlar was a much stronger material than Doron and provided more protection. Although the Doron and Kevlar vests were not called "bullet proof", they could stop many pistol rounds, and even rifle rounds that were ricochets or had been fired a long distance. The tougher Kevlar fiber and better layout of the vest reduced casualties to the torso by over 70 percent (versus troops without the vest.) But the troops wearing a vest were still vulnerable to high velocity bullets (from AK-47s, M-16s and 7.62mm machine-guns). Being "bullet-proof" was important in a different way than having all that protection from fragments. The biggest danger from bullets was when you were attacking, when the enemy could actually see you, and shoot at you. This is the scariest part of being an infantryman. It's bad enough when you're in a foxhole or behind a wall getting shelled. At least you have some protection, and the older, fragment proof, protective vests were much appreciated in these situations. But when you were out in the open, being a little bit bullet proof makes a big difference to morale and motivation.
By the late 1980s, it was possible to make truly bullet proof vests using metallic inserts. But the inserts were heavy and so were the vests (about 25 pounds). Great for SWAT teams, but not much use for the infantry. But in the 1990s, additional research produced lighter, bullet proof, ceramic materials. By 1999 the U.S. Army began distributing a 16 pound "Interceptor" vest that provided fragment and bullet protection. This, plus the 3.3 pound Kevlar helmet (available since the 1980s), gives the infantry the best combination of protection and mobility. And just in time. Since the end of the Cold War, more of the situations U.S. infantry find themselves in involve lightly armed irregulars who rely more on bullets than bombs. The bullet proof vest eliminates most of the damage done by the 30 percent of wounds that occur in the trunk (of which about 40 percent tend to be fatal without a vest). The Kevlar helmet is also virtually bulletproof, but it doesn't cover all of the head (the face and part of the neck is still exposed). Even so, the reduction in deaths is significant. Some 15-20 percent of all wounds are in the head, and about 45 percent of them are fatal without a helmet. The Kevlar helmet reduces the deaths by at least half, and reduces many wounds to the status of bumps, sprains and headaches. Half the wounds occur in the arms and legs, but only 5-10 percent of these are fatal and that won't change any time soon. Thus since Vietnam, improved body armor has reduced casualties by about a third. The protective vests used in Vietnam and late in the Korean war reduced casualties by about 25 percent since World War II, so the risk of getting killed or wounded has been cut in half since World War II because of improved body armor. Much better medical care (especially rapid evacuation of casualties by helicopter) has helped reduce the ratio of dead to wounded from 3:1 during World War II to 5:1 today.
The Interceptor vest was an improvement in other ways. It was easier to wear, and was cooler in hot climates because you could more easily adjust it to let some air circulate. You could also hang gear from the vest, making it more a piece of clothing. It's still hot to wear the vest in hot weather, but if you're expecting a firefight, it's easier to make the decision to wear the vest. You know it will stop bullets. U.S. troops who have fought in Afghanistan, and hit with rifle bullets that would have penetrated earlier vests, are already spreading the word throughout the ground combat community.
In a little heralded event, the U.S. has finally produced a lightweight bulletproof vest. For the first time since the introduction of firearms five centuries ago, the infantry have some real protection from bullets. Between 1999 and 2003, the U.S. Army will distribute 54,000 of the $1,700 Interceptor vests to infantry units. Another 22,500 CBA (Concealable Body Armor) vests (that can be worn under civilian or military clothing) are also being distributed to Special Forces, MPs and security personnel. The CBA is basically a lighter version of the Interceptor, without the ceramic plates to stop high power rifle bullets. The CBA will stop most pistol bullets.