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A 1915 French Army helmet does a better job protecting infantry from overhead shock blasts than its cutting-edge 21st century counterpart, a new study has found.

Simulating overhead explosions, researchers at Duke University compared the shock-resistance of the U.S. military's current combat helmet to three historical models. They found that France's First World War helmet, the "Adrian," protected the best against shock waves from above — likely because of its distinct crest.

Joost Op 't Eynde, a researcher in the Injury Biomechanics Laboratory at Duke and author of the new study, says combat helmets have not traditionally been designed to protect the head from shock waves. Impact from shock waves can cause traumatic brain injury.

Op 't Eynde discussed the findings with As It Happens host Carol Off.

Joost, what made you want to put old-time metal army helmets up against modern U.S. models?

So neither the modern helmets nor the historical helmets were designed to protect against shock waves. So we kind of wanted to provide a reference, kind of take a step back and just see how helmets really perform in general against shock waves.

French President Raymond Poincaré visits the frontline during the First World War, wearing the Adrian. (AFP via Getty Images)

And what do you mean by shock waves?

The sharp disturbance in the air that is caused by an explosion. So when we think about an explosion, there's all kinds of material being launched that could potentially injure somebody or there could even be a fireball that might burn somebody. But one important mechanism of injury is actually the shock that is formed in the air itself that can also cause injuries.

I presume we didn't put real people out there in two different helmets to see how they would survive. So how did you do the experiment?

We used a dummy head, like a dummy that they used in crash tests for cars. And so we put different pressure sensors at different locations on the head to measure the pressure of the wave that hits the head, and then we placed different helmets on … to see how that changes.

This helmet has a crest on the top of the head, kind of going from the front to the back. And this crest might have been partly ornamental, it might have been partly to deflect shrapnel, but this seems to have some effect on the results. - Joost Op 't Eynde

Where did the helmets come from? What were the various models that you tried?

We had three models from the First World War. We had a French helmet from 1915, [the Adrian], a German helmet from 1916, and then a helmet that was used by both the British and American forces: the Brody helmet.

And then we tested the advanced combat helmets, which is what the U.S. Army currently uses as their helmet for their soldiers.

A French infantry soldier wearing the newly-issued M15 Adrian helmet, August 1915. (Photo by Hulton Archive/Getty Images)

What did you find was the best protection against these shock wave blasts?

Specifically the scenario that we tested, which is kind of a blast coming from overhead … we were very surprised to find that the historical French helmet from 1915 resulted in lower pressures at the top of the head compared to these other historical helmets and the current U.S. helmet.

So the old French helmet was better even with whatever modern technology went into the contemporary American helmet?

Yes. So, there's a lot of technology in the modern helmet, but that technology was not put in there with shock waves in mind. So if you're talking about any other kind of protection such as protection against different bullets, like rifle rounds or handgun rounds, or against any kind of blunt impact — a fall or a hit — the modern helmet is vastly better than any of the historical ones.

And I would also like to stress that in our study we specifically looked at one scenario, where the blast is coming directly from over the head, and we only found that difference at the top of the head.

So at any of the other locations we had pressure sensors — at the ears, at the back of the head, at the eyes, the French helmet did not perform better. In fact still an interesting result is that all helmets kind of performed similarly, the modern one as well as the historical ones.

Researcher Joost Op 't Eynde says the modern U.S. helmet is much safer than the historical models overall, but the 1915 French Adrian better protected against overhead shockwaves. (TAUSEEF MUSTAFA/AFP via Getty Images)

When it comes to a bullet, or shrapnel ... something hitting you, which helmet was best for in those conditions?

So we didn't specifically test that, but it is widely known that … a modern advanced combat helmet is a lot better for it for these scenarios.

What is it, you think about this French 1915 helmet that could take the shock waves better?

This helmet has a crest on the top of the head, kind of going from the front to the back. And this crest might have been partly ornamental, it might have been partly to deflect shrapnel, but this seems to have some effect on the results.

It might deflect the wave around the head, rather than hitting straight on, or it might just provide an extra layer of protection because right at the top of the head there's two layers of steel one for the crest and one for the helmet itself. But yeah that seemed to change the results.

Wounded French infantrymen are led by comrades and escorted by British soldiers from the second Battle of the Marne, July 1918. (Three Lions/Getty Images)

So this specifically these shock waves just so people understand … what effect would it have on you or me if we were wearing these helmets and went into these shock waves?

So traumatic brain injury can be caused by these shock waves. Symptoms similar to concussions, and there could be short-term effects and long-term effects — a lot of that is still very much unknown.

And it's also kind of an invisible injury. Because you might not see any external injuries while the person might feel very injured and might be seriously impaired just because of what the shock does to their brain.

OK so if you were being sent into battle, or into war, which helmet would you want to go in with?

I would definitely prefer the modern helmet … just for the all around protection it provides.

This interview was produced by Chris Harbord. Post written by Sarah Claydon. Q&A shortened for length and clarity.