In the Super Sagas, Doc and his men use bulletproof undergarments that are composed of light metallic chain-mail. These can garments can range in size from a torso protecting vest to long-johns with arm length sleeves. They usually are depicted as protecting the chest and abdomen. Even when they stop a bullet, the kinetic energy is still depicted as causing bruising or even cracking ribs underneath. The degree of protection provided by these undergarments varies in different stories and seemed to increase over time. In the post WWII story The Ten Ton Snakes, the vest is described as capable of protecting a man from a 30-06 military rifle shell at point blank range. In this article, we will discuss what a bullet proof vest is and what technologies Doc Savage had to provide in order for the protective undergarments to function as described in the story.
Ordinary bullets damage the body in two ways. First there is penetrating trauma where the bullet enters the body and directly damages internal structure. This is the most devastating effect of the bullet and the one most like to induce a fatality. Such internal trauma can in fact cause virtually instant death. The second type of injury is from kinetic trauma which can be transmitted to tissues which have not been directly in contact with the bullet. Modern high-velocity military rounds that enter the body at speeds in excess of 2000 feet per second can induce shock waves in soft tissue that disrupt cells and blood vessels and devitalize tissue for several centimeters around the bullet's path in tissue. In cases where body armor is worn, the impact of the bullet can still induce serious injury to bones and soft tissue that can be life threatening even though the bullet does not penetrate the skin.
So the goal of any body armor is to not only prevent penetration but also to attenuate the kinetic energy of the bullet to prevent its transmission to the body.
A plain chain-mail vest will likely prevent penetration but it will do little or nothing to attenuate the kinetic energy of the impact. It would therefore be necessary to have some type of padding or some rigid plates to distribute the force of the impact over a larger area. In the early 1930s, the usual weapon of the criminal classes was a .32 caliber or .38 caliber pistol. Such rounds were effective at close range but they did not have much knock down power. A simple chain mail vest with a padded backing would have been enough to prevent penetration and attenuate the force of the impact. But when you got up to the .38 special and the .45, the chain mail would have been hard pressed to stop penetration point blank and the force involved would cause contusion injury through any conceivable simple padding.
Modern bullet proof vests use woven plastic polymers such as Kevlar over a backing that will sometimes contain hardened metal or ceramic plates. Metal plates may deform under impact and undergo metal fatigue. Ceramic plates shatter and absorb kinetic energy by doing so. In both cases, the vest is permanently altered and may provide the same protection after more than one or two bullet impacts. The problem with the polymers is that such vests will fail if they get wet since water helps to lubricate the bullet through the weave and can chemically disrupt the polymer molecules themselves. And they are only really effective against pistols up to the .357 Magnum and the .45. Larger pistol shells like the .44 Magnum or the .454 Casull and rifle bullets like the 30-06 will both penetrate such vests and deliver significant kinetic damage. There are more sophisticated armors now that use kinetic-reactive plastics and even spider-web material which change their tensile strength and rigidity under stress. In some materials, the introduction of a rapid kinetic jolt alters the viscoelasticity of the material so that the entire vest goes rigid attenuating the force of the impact over a very large surface area.
The undergarments Doc's men wore were supposed to be light weight but containing metal mail. A good closely woven metal mail would provide excellent penetration protection and would minimize metal fatigue in the impact areas. If the alloy were properly formulated it would also become harder under rapid stress. (There are several alloys known today that will do this.) This would solve the penetration problem. But this would also require a padded backing material to attenuate the kinetic impact. I propose that the metal mail was worn over a cloth under garment with an internal cotton lining and an external plastic polymer weave that became rigid over a large area upon sudden impact. Such a polymer may have been sealed against water to prevent degradation of performance in harsh conditions. The use of the metal mail would also guarantee protection while wet. Theoretically such a vest could give the performance described in the Super Sagas even against 30-06 ammunition.
The technology that Doc Savage had at his disposal was always anywhere from 30 to 60 years ahead of its time. We are only now contemplating making a protective garment with the above performance characteristics but we are still using polymer weaves to prevent penetration. Maybe Doc knew better and an external covering of woven metal-alloy mail with varied tensile strength under stress is the way to go.