Army engineers design a prototype mechanical arm to reduce the felt weight of carbines and machine guns

The U.S. military is testing the real-life version of the mechanical arm from the second Aliens movie, the one that helped Private Vasquez bear the burden of her massive machine gun. An article on explained that the “Third Arm” will likewise decrease the weight of a soldier’s weapon, making it easier to carry and improving aim.

Looking rather like a human arm sans hand, the lightweight load-bearing device weighs around four pounds. One end of the mechanical arm is attached to the waist belt of its wearer. The other end is connected to the soldier’s weapon, which can be a carbine or a much bigger gun.

The multi-jointed limb redistributes the weight of his or her weapon throughout the body in a more even manner. This lightens the strain on the arms of the service member.

A lighter weapon is easier for a soldier to carry and hold steady over long periods of time. The latter means the aim of the user is also improved, as his hands and arms are not shaking from the effort of supporting his weapon.

While mechanical, the Third Arm does not require any power to operate.

“It can help stabilize the weapon and take the load off of their arms,” explained Army Research Laboratory (ARL) mechanical engineer Dan Baechle during a recent press conference. “It’s made from composite materials to make it as light as possible but also to ensure the range of motion that soldiers need.”(Related: Army researchers develop A.I. tech that helps U.S. soldiers learn 13x faster than conventional methods.)

New load-bearing mechanical arm can help soldiers tote big machine guns with ease

The ARL also released a video that showcased the capabilities of the new mechanical limb. A volunteer equipped with the Third Arm and an M4 carbine sprinted through the Urban Terrain testing ground of the Aberdeen Proving Ground in Maryland.

In addition to carbines, the arm can also bear the burden of much bulkier machine guns. Baechle said that the ARL tested the Third Arm with the M249 light machine gun – which weighs in at 22 pounds (10 kilograms) – and the bigger M240B medium machine gun – an automatic weapon that tips the scales at 27 lbs (12 kg).

The Third Arm is part of a movement to improve the capability of the individual American soldier. As a partial “load-bearing exoskeleton,” it falls under the “sustaining” objective of the overall U.S. Army modernization program, as it reduces exhaustion and thus helps keep soldiers in the fight.

During the 2017 pilot study of the Third Arm, an earlier version of the device stopped the wearer from lying down on the ground in a prone position. Despite this drawback, the prototype device was able to increase the user’s shooting accuracy while also reducing the fatigue.

The ARL engineers fixed the issue regarding the inability to enter the prone position. In the exhibition video, the tester went from a sprint to a dive and stayed prone on the ground to avoid getting noticed or shot at. During the aggressive maneuver, the Third Arm did not get in the way of its user’s movement.

The Third Arm will undergo further testing in the later half of 2018. It will be subjected to a variety of shooting scenarios.

Baechle said he and his colleagues are implementing the feedback from the soldiers who tested the device. Their aim is to make the Third Arm comfortable for users as well as effective in combat. The final version may not look anything like the prototype in the video.

Read more articles about the latest modernization efforts of the U.S. military at

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