Body armor, apart from
airmen flak vests, has not been given
much attention by the U.S. military throughout history.
This has been due to a combination of technology, money,
and a lack of being “sexy”, or “digitized.” 
The technology to develop effective body armor that men are capable of actually moving around in has only come out in the last 20 years. It must be remembered that the issue of body armor is not only stopping a bullet, but also displacing 500 to 1000 foot pounds of bullet energy in such a manner that it won’t crush the upper torso and liquefy the innards of the wearer. Kevlar and Spectra allow the ability to stop low energy rounds, usually up to about 44. Magnum caliber, but will still result in broken bones. Developments in ceramics are what have made it possible to stop .30 caliber, and even one claim of .50 caliber Armor Piercing ammunition (although I question whether a person could survive the impact, as a .50 caliber round has about 4000 foot pounds of energy at the muzzle, and doesn’t drop much after that.) The only drawback to ceramics are that they are rigid, which restricts mobility, are still relatively heavy (between 4 and 10 pounds per plate), and their method of dispersing energy from a round is by shattering, which makes each plate a one-shot deal.
Practicality has been greatly improved in recent years, as an example, the PASGT armor (really a flak vest) is only capable of stopping shrapnel, plus it tends to be a bit bulky, especially when trying to fit web gear over it. The new Interceptor body armor being fielded provides protection from both shrapnel and bullets up to 9mm, plus it can mount ceramic plates for protection against up to .30 caliber rounds. The basic Interceptor vest is about a half pound lighter than the PASGT, and is designed to be compatible with web gear.
The biggest problem with body armor is getting sized comfortably. The PASGT vest is very stiff and comes in “one-size-fits-all.” This results in vests that are either too big or too small, too long or too short, and the vest tends to shift around a lot while moving, especially when you put something like a ruck on. They are very hot in the summer, but can be of some insulating value in the winter, as well as providing some back support with heavier loads. Females with significant endowments can also encounter problems with body armor vests.
My suggestion from the issue of sizing is to issue personnel a custom fit body armor vest in Boot or Basic as part of their initial uniform issue, to stay with them throughout their career. Since everyone would get one, everyone would be required to turn one in upon separation or retirement, and anyone who didn’t would be held financially liable for it. This would allow bases to keep only enough on hand for replacements and repairs. Second, make the vests a modular design, with Extra Small through Extra Large front and back panels that are slightly narrower than currently made, then have various sizes of side and shoulder panels for fitting it properly around the person. The shoulder panels and the back of the side panels could be attached and fitted with 550 cord, in the same manner as on the current issue LBV, and the front of the side panels would use zippers and Velcro to cover the zippers. The use of the 550 cord would allow the vest to be made snug-fitting, while also allowing it to be made larger to accommodate cold-weather gear. The 550 cord could also be easily cut by a medic to disassemble the vest quickly, and could be used for survival purposes. The use of zippers on the sides would allow the use of a single panel on the front, while still making it easy to get on and off.
Money is always an issue, and body armor is like training, nobody wants to pay for it when they can’t see a tangible benefit. Or to put another way (the traditional American military way), we don’t want to spend the money on it until a whole bunch of people get killed, then rush and get what we can and send it out to the field, and when the crisis is over, then forget about it again. This is where money, and “sexy” or “digitized” merge. Generals, and aspiring generals, want things that go fast, look cool, make lots of noise, or have lots of cool gadgets and doo-dads. This is from a combination of needing to sell it to intellectually and military-doctrinally challenged politicians; down-payments on post-retirement positions as “advisors”, lobbyists, industry-reps, etc.; down-payments on the next star; one-upping their counter-parts from their sister-services; and impressing their wives, girlfriends, fellow-travelers, and the like.
Body armor isn’t “sexy”, it just sits there. Most modern generals don’t need it because they don’t even think about getting anywhere near where the shooting is going on, so it’s not on the top of their mind; the commanders of combat units would love to get it, but in order to, would have to either spring from his own pocket, or cut insignificant things like rations, ammunition, medical supplies, etc., from a couple of budgets, plus probably have to deal with multiple levels of the chain of command to explain why he was ordering non-TO&E equipment separate from the rest of the Battalion, Brigade, etc.
The acquisition of Interceptor body armor is a great step forward. It would be great to get it throughout the entire force, but just making sure that it gets to the grunts would be a big step. Issue of this vest can also help to alleviate the shortage of flak vests for support units and the Air Force, if somebody thinks to send them there instead of surplus sales.
Check these links for more body armor info:
Letters
Body Armor and Utility Blouse
As a Marine who has deployed to hot climates, I can attest that body armor worn over the utility blouse is hot. The Generals don't let us shed the blouse and just wear the vest over a T-shirt because it looks too casual on TV. What occurred to me EVERY DAY is why the utility blouse? We always have to wear body armor in combat zones, so why have four useless pockets on a light jacket underneath? Just add some durable denim sleeves to the body armor vest and leave the utility blouse back in garrison.
Hank Malanowski