Remember that shield that Captain America uses? The one that deflect bullets?

Well, the U.S. Army wants the same kind of shield. But not for the infantry. It's a shield for tanks.

The Army is asking industry to to develop moveable tank armor that, like Captain America's shield, can stop an incoming missile.

The specifications call for a mechanism that can move an armor panel, at least 1-foot-square in size, to a distance of 10 inches horizontally. And do so within less than five seconds. The armored panel would be an extra layer of protection attached to the outside of the vehicle, and remotely controlled by the crew.

The proposal is somewhat vague, but the idea appears to be armor that can be rearranged like a puzzle. So that, for example, a tank attacked from the sides or rear can shift additional armor to shield its vulnerable flanks.

The moveable armor project is what the Pentagon calls a Small Business Innovation Research, or SBIR, proposal, where the government puts out an idea and challenges industry or academia to solve it. The impetus here is to break out the trap that has hemmed in tank designers since the first "landships" clanked across the trenches of World War I.

The problem is this: as anti-tank weapons become more powerful, the first solution is always to design a tank with thicker armor. But this adds to the vehicle's size and weight, which makes it a bigger, more expensive machine that eats more fuel yet offers less mobility. Another solution is to just add extra armor to specific sections of a vehicle, but this presents its own problems: the German Panther tank of World War II had thick frontal armor, which was the area most likely to be hit, but this was only achieved by making the side armor weak.

The logical culmination of this process is that you either end up with a tactically useless moving pillbox like the German Maus, or eventually the tank-killers win, because it's easier to design more powerful projectiles than it is to build a tank that can resist them.

“Conventional armor systems are essentially static and unable to respond to unanticipated changes in threats deployed against the system; essentially the Army has limited potential to increase the capabilities of current static armor recipes in order to balance size, weight, and performance requirements,” the Army concedes.

This is becoming an issue as the U.S. military considers its next generation tank to replace the Abrams. Moveable armor may be too difficult to retrofit to existing vehicles like the Abrams or Bradley. But it is very likely to be part of DARPA's Ground X-Vehicle Technologies (GXV-T), the shape of American tanks to come.

DARPA's preliminary concept envisions a four-wheel vehicle, half the size and weight of a current tank, that somewhat resembles one of those NASA rovers exploring Mars. And one way DARPA plans to achieve a lighter but more survivable tank is through “active repositioning of armor,” according to the agency's description.

One interesting wrinkle is that the Army proposal explicitly prohibits any solution that is an active protection system. That means the Army wants to avoid anything like Israel's Trophy gear, which shoots down incoming rockets with a shotgun blast of projectiles. The Army suggests one reason for this stipulation when it calls for moveable armor that “shall not pose harm to dismounted personnel.” Detonating explosives to stop a missile, as some tank defense systems do, may save the vehicle -- but only at the risk of injuring nearby infantry that are supposed to be protecting the tank.

The Army also says that it does not want any defense system that doesn't protect the vehicle if the system fails. In other words, shotgun shells and the like may or may not shoot down a missile. But there's no protection as reliable as instantly putting an extra layer of armor between you and a warhead.

Here is the main portion of the Army's moveable armor proposal:

OBJECTIVE: Develop and demonstrate a model for a mechanism capable of moving an armor panel of at least 1 square foot with an areal density of 100 pounds per square foot (PSF) 10” horizontally in less than 5 seconds.  The movement is intended to be repeatable and controlled from the interior of the vehicle and shall not pose harm to dismounted personnel.

DESCRIPTION: Conventional armor solutions currently being integrated are “not adaptable” in providing increased threat capability and protection from a greatly expanded set of threats.  A solution is needed for threats that are not feasibly addressed with conventional armor systems.  Conventional armor systems are essentially static and unable to respond to unanticipated changes in threats deployed against the system; essentially the army has limited potential to increase the capabilities of current static armor recipes in order to balance size, weight, and performance requirements.

Increased threat defeat using conventional armor is prohibitive due to the significant weight burdens associated with increased protection. Any increase in weight has secondary effects such as limited off-road mobility and increased logistics burden.

This SBIR topic solicits new, innovative approaches to incorporate mechanisms into an armor system to provide protection against increased threats.  For the purpose of this effort the system shall be designed to interface with a 1” plate of Rolled Homogenous Armor (RHA) Plate that represents a surrogate vehicle structure.  The mechanism needs to be capable of moving a 100 PSF armor panel 10 inches horizontally in less 5 seconds.  The mechanism needs to be able to withstand automotive loading as well as environmental conditions typical of a combat vehicle. The proposal should discuss in detail how the system could be incorporated onto a vehicle platform and what the projected Space, Weight, Power, and cooling (SWAP-C) at the vehicle level.

The proposal shall not include a system that could be describe as an Active Protection System (APS).  A system is considered an APS system if any of the two statements apply: 1. A light-weight hit avoidance vehicle defense system which, when integrated on a ground combat vehicle, can detect, track; and then interdict by diversion, disruption, neutralization, or destruction of incoming line-of-sight threat munitions.  2.  A system that deploys a counter-measure that does not providing any inherent protection to the vehicle system when the counter-measure does not perform as designed.

Michael Peck is a frequent contributor to the National Interest and is a regular writer for many outlets like WarIsBoring. He can be found on Twitter and Facebook.

Image: An anti-tank missileman fires a TOW Missile System. Flickr/U.S. Marines