bullets containing lead cores, however the same panels may easily be defeated by 7.62×39mm armor-piercing bullets containing hardened steel penetrators. Bullet-resistant materials (also called ballistic materials or, equivalently, anti-ballistic materials) are usually rigid, but may be supple. They may be complex, such as Kevlar, UHMWPE, Lexan, or carbon fiber composite materials, or basic and simple, such as steel or titanium. Bullet resistant materials are often used in law enforcement and military applications to protect personnel from death or serious injury. In 2018, the US military began conducting research into the feasibility of using artificial silk as body armor. Uses Bullet-resistant body armor has been in use since about 1984. When law enforcement began wearing body armor, there was a dramatic drop in officer deaths, saving over 3,000 lives. The National Institute of Justice first developed standards for ballistic resistant body armor in the 1970s. The standards have been revised five times since 1984. The National Law Enforcement and Corrections Technology Center tests body armor to assess its compliance with the standards and publishes the results. There are many applications for bulletproofing, some of which include: Aerospace Armored car Armoured fighting vehicle Bank vault Bombsuit Bulletproof glass Bulletproof vest Bulletproof helmet Liquid Armor Military vehicle Panic room Plastic armour Riot shield Safe Classification There are various tests which items must pass before being classified as bullet-resistant. These tests specify the detailed characteristics of bullets which the material or object must be resistant to. For example, the U.S. National Institute of Justice standard 0104.04 for bullet-resistant vests specifies that a Type II vest must not deform clay representing the wearer's body when hit by an 8.0 g (124 gr) 9 mm caliber round nosed full-metal jacket bullet travelling at up to 358 m/s (1175 ft/s); but a Type IIIA vest is needed for protection against the same bullet traveling at up to 427 m/s (1400 ft/s). In both cases, the vest is not required to protect against a second hit within 51 mm (2 inches) of the first. References Armour