For a long time, in order to improve the survival rate on the battlefield and reduce the casualties of soldiers, the US military began to use a variety of individual bulletproof equipment, from the small-scale trial of M9152 in the Korean War to the large-scale M1955 and M1969 allotment in the Vietnam War. In fact, these bulletproof vests can't prevent the direct attack of bullets. At best, they can only resist the attack of grenade fragments, ricochets, or shell fragments that are indirectly hit.

It was not until the emergence of Kevlar materials in the 1980s that the later PASGT vests had a certain degree of ballistic performance, but they were limited to resist the penetration of projectiles equivalent to 9mm caliber pistols at a certain speed and angle. Since the birth of rifled rifles and bullets, the performance of guns has been far beyond the development of protective equipment. Many bullets are difficult to resist even with a certain thickness of steel plate. In addition, the load that soldiers can bear is limited, and heavy bulletproof equipment will only wear soldiers. His physical fitness and mobility are meaningless for the improvement of battlefield protection.

In order to obtain better bulletproof effects, lightweight and strong bulletproof materials have always been the target of human exploration. OTV, which appeared after PASGT, became the first U.S. military's first official bulletproof vest with real ballistic performance. The reason for this ability is the emergence of SAPI-Small Arms Protective Insert. OTV uses hard silicon carbide ceramic plates to obtain higher protection capabilities based on the limited protection of soft Kevlar materials.

According to military requirements, a standard-sized SAPI must be able to effectively withstand the impact of a 7.62mm caliber M80 projectile flying at a speed of 841 meters per second, and each SAPI must be able to withstand three such impacts to be qualified. This also means that the OTV vest equipped with SAPI can resist the attack of 7.62×39mm projectiles fired by the AK47 rifle, which is definitely a qualitative improvement for individual protection!

In the following years, the threats faced by the U.S. ground forces did not diminish, so the U.S. Army put forward the concept of the next generation of shields, XSAPI. The Army required this new generation of hard shields to be more flexible, convenient and systematic. The protection area is larger, and the weight cannot be increased. Because of the end of the war on terrorism, XSAPI did not formally appear in the US military's sequence, but the design of XSAPI has not stalled. Once the US military faces new threats again, this next-generation light weapons shield will be quickly distributed and put into use.

Initially, the performance of the SAPI board used in the bulletproof vest represented by OTV did not get the rating of NIJ, the National Institute of Justice, because it was designed at the request of the military and tested in accordance with the military's standards. The standard formulated by the party is not equivalent to the NIJ test standard, but after SAPI has achieved a series of successes on the battlefield, the civilian and law enforcement markets also favor it, so NIJ also conducted a series of standard assessments.

In other words, SAPI does not guarantee that the user will be unharmed, only that the user will not be fatally injured. In many instances, SAPI escaped a catastrophe, but because of the powerful force of the projectile, the non-lethal second Secondary injuries are very common. In order to reduce this kind of injury, the US military generally requires that bulletproof vests must be soft and hard, that is, use hard SAPI boards in addition to the soft protective layer, which can effectively reduce the occurrence of secondary injuries. .

Very often we see that many special forces soldiers use bulletproof vests that look very small. The size of this vest is basically the size of a SAPI board. These special forces soldiers are often inconvenient in logistical support when performing missions behind enemy lines. If they carry a lot of weight, they will definitely affect their operations, but if there is no protection, they will encounter the enemy. It is very likely that they will not be able to protect themselves (the four SEAL soldiers in the "Red Wings" in 2005 did not use protective gear), so this kind of small and properly protective gear is welcomed by them.