Body Armor Statistics and Plate Selection
Part 1 – Military:
It should go without saying that military body armor must be designed to prevent military injury. Patterns of wounding are not static — they’re situational and evolve in response to the arms, armor, and doctrine employed — so this is an ongoing effort. Fortunately, the US Military keeps reasonably good public records, which can be summarized:
Site of injury:
Head/Neck – 21%
Upper torso – 13.9%
Abdomen – 8%
Extremities – 58%
Head/Neck – 16%
Upper torso – 13.4%
Abdomen – 9.4%
Extremities – 61.1%
Head/Neck – 30%
Upper torso – 5.9%
Abdomen – 9.4%.
Extremities – 54.5%
Site of injury:
Gunshot wound – 65%
Explosive or fragmenting munition – 35%
Gunshot wound – 27%
Explosive or fragmenting munition – 73%
Gunshot wound – 35%
Explosive or fragmenting munition – 65%
Gunshot wound – 19%
Explosive or fragmenting munition – 81%
The majority of casualties in OEF/OIF were on account of improvised explosive munitions — IEDs. They accounted for both the majority of injuries and the majority of soldiers KIA. Generally, most of the serious/fatal injuries were blast wave injuries; most of the minor injuries were fragment injuries.
Historically, in the WWII and post-WWII eras, mortars, artillery shells, and other fragmenting munitions were responsible for the majority of combat casualties. In any future peer or near-peer conflict, they’ll likely retake their crown, and patterns of wounding will at least superficially resemble those from WWII. Indeed, although reports are still incoming and the picture is not yet entirely clear, reports from the 2020 Nagorno-Karabakh Conflict between Armenia and Azerbaijan indicate that precision artillery and drone strikes were responsible for a preponderance of casualties on the losing Armenian side.
There is little current US Military data with respect to the precise anatomical location of those injuries, but a report titled “Wounding Patterns for U.S. Marines and Sailors during Operation Iraqi Freedom, Major Combat Phase” provides some insights. It analyzed a cohort consisting of 97% Marines and 3% sailors who were wounded in action, during the invasion phase of OIF, from March 23 through April 30, 2003:
- 46% of injuries were due to exploding munitions, 25% to small arms, and the remainder were due to accidents, falls, or “other.”
- Of the small arms wounds, roughly 5% were to the abdomen, 8.5% were to the chest, 1.2% were to the back, 1.2% were to the neck, 1.2% were to the head, and the remainder were primarily to the legs (31.7%) and the arms (42.7%).
This is interesting if it’s compared to a different paper. In “accurate anatomical location of war injuries: analysis of the Lebanon war fatal casualties and the proposition of new principles for the design of military personal armour system,” Gofrit et al. analyzed 405 penetrating war injuries in 164 Israeli Army fatalities in the 1982 Lebanon war.
- There were 290 shrapnel and 115 bullet injuries overall.
- Roughly 50% of the shrapnel injuries were to the torso, and roughly 20% to the extremities. The remainder, ~30%, was to the head, face, and neck.
- Nearly 40% of bullet wounds were to the torso, and 45% were to the head, face, and neck. The extremities accounted for just over 15%.
- Infantrymen were most likely to be struck by bullets. 39% of injuries in infantrymen were on account of bullet impact, and 61% on account of explosive or fragmenting munition. In contrast, nearly 85% of tank crewman injuries were on account of explosive or fragmenting munition, and just 16% were on account of bullet impact.
- 94.4% of bullet wounds were anterior — that is, to the front of the body.
- 91% of all injuries were to the front of the body.
Admittedly, that’s an old report, and describes injuries that resulted from a style of near-peer open field warfare that has been upended by guided munitions, drones, and so forth. (Today, nobody is quite sure what peer or near-peer conflict between advanced nations would even look like.) More recently, in “Operational mortality of UK service personnel in Iraq and Afghanistan: a one year analysis 2006-7,” Hodgetts et al. analyzed 76 trauma-related fatalities in UK troops in Iraq and Afghanistan between 1st Aprl 2006 and 31st March 2007.
- 75% of deaths were the result of hostile action, with the rest the result of accidents.
- Overall, 67% of hostile action deaths were due to blast or fragmentation, 33% were due to gunshot wounds.
- In Iraq, 76% of hostile action deaths were due to blast and fragmentation, and 24% were due to gunshot woulds.
- In Afghanistan, 57% of hostile action deaths were due to blast and fragmentation, and 43% were due to gunshot woulds.
- Head injuries were present in 42% of hostile action deaths, torso injuries in 40%, neck injuries in 24%, abdominal injuries in 16%.
In comparing the first report with the second two — where the first report only focused on those wounded in action and the latter two focused on those KIA — it’s clear that small arms injuries to the extremities are rarely fatal, whereas wounds to the head, neck, or torso are frequently fatal.
This data also seems to suggest a few things:
First, that improvements to helmet design are at least as pressing and as important as improvements to body armor systems. The current combat helmet does not provide adequate protection from blast wave exposure, which is the primary mechanism of injury today, and is sure to remain a dominant mechanism of injury long into the future.
Second, given the overwhelming preponderance of fragmentation injuries, especially to the limbs, improvements in soft armor materials and systems, guided towards improved armor coverage, are of key importance. And, of course, technological improvements in this area will also result in better, lighter hard armor plates. This may also reduce the casualty burden associated with small arms wounds to the extremities, which are apparently fairly common but do not result in substantial morbidity.
Further, with the data from OIF and the data from Gofrit et al, it would seem that the overwhelming preponderance of bullet injuries are anterior — that is to say, when bullets strike, they are 10x to almost 20x more likely to enter through the front of the body. It may make sense to consider pairing a larger and heavier armor plate in the front, with a smaller or lighter armor plate in the back. This is indeed quite an ancient practice — one which Alexander the Great was known to promote — and was recently employed by the Soviets.
More data is required, but, though admittedly unorthodox, this doesn’t seem like an obviously bad idea; full body armor does not exist, and one must prioritize coverage based on (a) where shots are likely to be particularly damaging or fatal, and (b) where shots are likely to hit. If shots in the back are indeed that uncommon, it stands to reason that the front armor plate is vastly more important than the rear armor plate, and should be made larger, stronger, etc., whereas the rear plate can be made smaller and thinner. That they are of equal weight and capability seems unreasonable, given that one may be ~10-20x more likely to be impacted than the other.
Then there’s the famous WWII anecdote: When trying to figure out how to optimize armor design for bomber aircraft, the US military and Columbia University’s Statistical Research Group examined a number of bombers that had returned damaged from missions. The military recommended that the parts of aircraft that had more bullet holes should receive more armor; the SRG countered that the least hit areas should receive more armor. This is because the military only considered the aircraft that had survived their missions – ignoring any bombers that had been shot down or otherwise lost, and thus also been rendered unavailable for assessment.
The bullet holes in the returning aircraft represented areas where a bomber could take damage and still fly well enough to return safely to base. Therefore, SRG proposed that the Navy reinforce areas where the returning aircraft were unscathed, inferring that planes hit in those areas were the ones most likely to be lost. This anecdote — which generally illustrates the concept of survivorship bias, and is considered formative to the field of operational research — has a clear parallel here. The arms and legs of infantrymen seem to take far more bullet impacts than other areas of their bodies, but soldiers KIA exhibit far more torso and head/neck wounds, and far fewer limb wounds. Bullet wounds to the limbs are apparently associated, generally, with low mortality, and limb armor is likely unwarranted unless it is extremely light. (Or, e.g., supported by a motorized frame.)
Like the military, the FBI keeps statistics on police officers murdered or assaulted in the line of duty (“LEOKA,”) and those records are fairly detailed. As of this writing, data for 2020 isn’t yet available, but to summarize the 2019 edition:
- 511 officers were killed from 2010 through the end of 2019.
- 471 of those were killed with firearms, 3 with knives, 5 were beaten or strangled to death, and 32 were run over with vehicles.
- Of those 471 killed with firearms, 343 (72.8%) were killed with handguns, 100 (21.23%) with rifles, 22 (4.67%) with shotguns, and 6 were hit by multiple weapons or the type of firearm is unknown.
- Of the 343 killed with handguns, fully 112 (32.65%) were killed by 9mm handguns. 75 (21.8%) by .40 caliber handguns. 46 (13.4%) by .45 caliber handguns. Those three calibers alone account for nearly 70% of all fatal handgun shootings. .38 and .380 account for another 48 deaths (14%). Over the past ten years, the .44 Magnum was only employed in one fatal police shooting (0.29%), the 10mm was also only seen once, and the 5.7x28mm was utilized in two fatal police shootings. There is a vast gulf between “common” and “uncommon” threats.
- Of the 100 killed with rifles, fully 38 (38%) were killed by rifles chambered in the ever-popular .223/5.56mm. 22 were killed by 7.62x39mm rifles. 6 by 5.45x39mm, though five of those were in one incident, the 2016 Dallas police shooting. 4 were killed by rifles chambered in .308. So those four rifle calibers are responsible for 70% of police fatalities, with .223/5.56mm responsible for more than the three others combined. Of the other 30 fatalities, 12 were due to an undetermined rifle threat, 7 were due to pistol caliber carbines firing .45 or 9mm, and the rest were due to hunting rifles chambered in .270, .25-06, or similar.
- Of the 511 officers murdered, 365 (71.5%) were wearing body armor at the time of their shooting. 344 of those were in uniform.
- Of the 471 officers killed via firearm. 270 (57.3%) were killed due to wounds to their head, face, or neck. 102 (21.6%) were killed due to wounds to their chest, and 23 (4.9%) due to wounds in their upper back. 23 were killed due to abdominal wounds, and 12 (2.6%) due to lower back wounds. 32 undetermined or unreported. The remainder to rare leg, groin, or shoulder injuries.
There are some takeaways for us here.
Given the overwhelmingly dominant presence of rifles chambered in .223/5.56mm on the casualty chart, hard body armor that doesn’t offer comprehensive protection from the full spectrum of .223/5.56mm threats, at all plausible velocities, is a poor investment. This is why NIJ’s .06 specification was inadequate, and why the NIJ’s forthcoming RF2 specification in .07 can’t come quickly enough.
Note that armor panels comprised solely of polyethylene typically fail when up against 5.56x45mm M855, which has a semi-hardened steel penetrator. Armor panels comprised solely of steel can fail catastrophically against fast-moving, lead-cored .223 and 5.56mm threats such as M193– and will also fail against .270 Winchester and .25-06.
Another thing: The overwhelming majority of handgun rounds employed in these shootings were Level II or sub-Level II threats. A Level II armor panel should be able to deal with just about all of them. Level IIIA is excessive; “protection from .44 Magnum with less than 44mm BFD” is frankly not worth the weight and thickness tradeoff.
Speaking of backface deformation, the FBI’s statistics continue to confirm something that we noticed some years ago: There has never been a single recorded death due to body armor backface deformation.
There are instances on record where officers wearing Level IIa vests were shot with heavy rounds, resulting in backface deformation estimated to have been in excess of 80-100mm, and those officers all survived, without exception. There was even a case where an officer wearing a Level IIa vest was hit at close range with buckshot from a 12 Gauge shotgun, resulting in an estimated 131mm of backface deformation. That officer survived with minor injuries. This was reported in a paper by Bir et al., titled “Behind Armor Blunt Trauma: Recreation of Field Cases for the Assessment of Backface Signature Testing.”
So, clearly, for most police and security personnel, Level IIIa armor is too much. Too thick, too heavy — ultimately, simply overbuilt for improved BFD performance against a threat that police officers are very unlikely to ever face.
Another thing that the data shows is that head shots are, by a wide margin, the main mechanism of fatal injury. This is, almost certainly, because police officers wear body armor but don’t usually wear helmets. Ballistic resistant headwear may need to evolve in response to this trend.