At that time, the military explored the possibility of using soft body armor manufactured from silk. The project even attracted congressional attention after the assassination of President William McKinley in 1901. But while these bulletproof vests garments were shown to be effective against low-velocity bullets (traveling at 400 feet per second (ft/s) or less), they did not offer protection against the new generation of handgun ammunition being introduced at that time that traveled at velocities of more than 600 feet per second. This, along with the prohibitive cost of manufacturing the garment ($80 each, which amounts to approximately $1,400 in 1998 dollars) made the concept unacceptable. Armor of this type was said to have been worn by Archduke Francis Ferdinand of Austria when he was killed by a shot to the head, thereby precipitating World War I.

The U.S. Patent and Trademark Office lists records for bullet proof vests dating back to 1919 for various designs of bullet resistant and body armor type garments. One of the first documented instances where such a bullet proof vest was demonstrated for use by law enforcement officers is detailed in the April 2, 1931 edition of the Washington, D.C., Evening Star, where a bullet proof vest was demonstrated to members of the Metropolitan Police Department. However, none of these designs proved entirely effective or feasible for law enforcement or corrections use.

The next generation of anti ballistic bullet proof vest was introduced during World War II. The "flak jacket," constructed of ballistic nylon, provided protection primarily from munitions fragments and was ineffective against most pistol and rifle threats. These vests were also very cumbersome and bulky, and were restricted primarily to military use. It would not be until the late 1960s that new fibers were discovered that made today's modern generation of cancelable body armor possible.