Aluminum vehicles can be lightweight, well-protected, and corrosion resistant, so why don't troops love them? Partially because there's a decades-old belief that their hulls catch on fire.
Aluminum has served in war since ancient times, but its most common application today is as armor, allowing for well-protected but light vehicles that can tear through rough terrain where steel would get bogged down. But aluminum has an unearned reputation for burning, so troops don't line up to ride in them under fire.
Crewmen in the coupla of an M-2 Bradley infantry fighting vehicle elevate the barrel during a 1987 exercise.
(U.S. Army Pfc. Prince Hearns)
Aluminum got its start in war as alum, a salt composed of aluminum and potassium. This was one of the earliest uses of aluminum in military history. Ancient commanders learned you could apply a solution of the stuff to wood and reduce the chances it would burn when an enemy hit it with fire.
As chemists and scientists learned how to create pure aluminum in the 1800s, some military leaders looked to it for a new age of weaponry. At the time, extracting and smelting aluminum was challenging and super expensive, but Napoleon sponsored research as he sought to create aluminum artillery.
Because aluminum is so much lighter than steel, it could've given rise to more mobile artillery units, capable of navigating muddy lanes that would stop heavier units. Napoleon's scientists could never get the process right to mass produce the metal, so the ideas never came to fruition.
But aluminum has some drawbacks when it comes to weapon barrels. It's soft, and it has a relatively low melting point. So, start churning out cannon balls from aluminum guns, and you run the risk of warping the barrels right when you need them.
Instead, the modern military uses aluminum, now relatively cheap to mine and refine, to serve as armor. It's light, and it can take a hit, making it perfect for protection. The softness isn't ideal for all purposes, but it does mean that the armor isn't prone to spalling when hit.
But aluminum's differences from steel extend deep into the thermal sphere. While aluminum does have a lower melting point than steel, it also has a higher thermal conductivity and specific energy (basically, it takes more heat to heat up aluminum than it does to heat up steel). So it can take plenty of localized heat without melting away.
An armored personnel carrier burns in the streets of Egypt during 2011 protests.
(Amr Farouq Mohammed, CC BY-SA 2.0)
So why don't troops love the stuff? It has a reputation for burning, for one. It's not fair to the material. Aluminum actually doesn't burn in combat conditions, needing temperatures of over 3300 Fahrenheit to burn and lots of surface area exposed to keep the reaction going.
(In industrial applications that rely on aluminum burning, the process is usually started by burning another metal, like magnesium, which burns more easily and releases enough heat, and the aluminum is crushed into a fine powder and mixed with oxygen so that the soot doesn't halt the reaction.)
But that hasn't stopped detractors from blaming the metal for all sorts of vehicles that were lost. The Royal Navy lost nine ships in the Falklands War, and three of them had aluminum superstructures. Aluminum detractors at the time claimed it was because the ships' aluminum hulls burned in the extreme heat after being hit, even though the ships had steel hulls and aluminum does not burn outside of very certain conditions.
U.S. Army armored vehicles leave Samarra, Iraq, after conducting an assault on Oct. 1, 2004.
(U.S. Army Staff Sgt. Shane A. Cuomo)
All these reports of burning aluminum were spurred on in the '80s and '90s by a very public fight between Army Col. James G. Burton, a man who didn't like the M113 in Vietnam and hated the M2 Bradley while it was under development. He repeatedly claimed that the Army was rigging tests in the Bradley's favor, tests that he said would prove that the vehicles would burn and kill the crew in combat.
In a book published in 1993, after the Bradley became one of the heroes of Desert Storm, he claimed that the vehicles survived because of changes made after those tests. But while the Army might have switched the locations where ammo was stored and other design details, they didn't change the hull material.
But, again, aluminum does melt. And the few Bradley's that did suffer extended ammo fires did melt quite extensively, sometimes resulting in puddles of aluminum with the steel frame sitting on top of it. This spurred on the belief that the aluminum, itself, had burnt.
The M2A3 Bradley is capable, but troops don't love its aluminum hull.
(Winifred Brown, U.S. Army)
But aluminum melts at over 1,200 Fahrenheit, hot enough that any crew in a melting aluminum vehicle would've died long before the armor plates drip off. Aluminum is great at normal temperatures, providing protection at light weights.
And so aluminum protects vehicles like the M2 Bradley and the M113 armored personnel carrier. The new Armored Multi-Purpose Vehicle that is slated to replace the M113 has, you guessed it, an aluminum hull. But while troops might enjoy the increased space, they'll probably leave off any discussion of the vehicle's material while bragging.
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