It weighs less than 1.8 kg (4 pounds), and consists of a mechanical appendage made out of carbon fiber composite that has one end attached to a carbon fiber plate that fits inside an armor plate pocket and the other end attached to a Picatinny rail on top of the gun.
[4] The project was an attempt to improve the marksmanship of soldiers by finding ways that would make the use of heavier, more lethal firearms and larger bullets easier to manage.
[2][5] The first prototype of was built in 2016 and first unveiled to the public in March 2017 at the Association of the United States Army (AUSA) conference in Huntsville, Alabama.
A pilot study was conducted in summer 2017, where the prototype was tested with six soldiers who wore electromyography sensors that recorded muscle activity with and without the Third Arm.
Changes included the mounting location, the addition of an extendable hinge plate that adhered to different body types, and refinements to the design that made it easier for the wearer to dive into the prone shooting position.