Dr. Leif Nelson, who worked on the development of the LUKE arm, said that the number of people who had lost arms relative to those who had lost legs was too small to spur private research and development. Thats when Darpa, along with the Department of Veterans Affairs, funded studies to develop the latest prosthesis. They in turn were able to enlist private companies, working with Dean Kamen, who invented the Segway.

Sensors, similar to the ones found in smartphones that automatically sense when the screen has been flipped, were strapped to a persons feet, enabling arm control by moving the foot side to side or back and forth. And for those who had lost an entire arm, motors at shoulder level enabled people to lift their arms above their head. The next step, Dr. Nelson said, was to develop on-skin sensors that would detect nerve signals and translate them into specific movements.

This is the first device that intuitively moves multiple joints at one time, he said. With other technology, you had to use the hand, then stop. Use the wrist, then stop. It wasnt fluid.

The arm, which will be commercially available through the manufacturer Mobius and sold to civilians too, will cost in the low six figures, though pricing is being worked out, officials said. An initial order of 10 has been placed for veterans.

Mr. Downs and Mr. McAuley were chosen as recipients based on medical necessity and because they participated in the research that led to the LUKE arms development.

Mr. McAuley, 70, who lives in Richmond Hill, Queens, where he cares for his mother, spent most of his post-military life without a prosthetic arm. I did one-armed stuff, he said. I tied my tie with one arm. I tied sneakers with one arm. I typed with one finger. I was strictly a one-sided person.

He participated in Darpas research project, he said, not so much for himself but to help others. Its given me hope for the future, he said. Its not that I want to be remembered, but I would like this to be an inspiration for people down the road.

Mr. Downs, a former Veterans Affairs official who lives in Maryland and is now a consultant to the Paralyzed Veterans of America, had long used a hook arm. But his new prosthesis will finally let him do tasks that require greater dexterity or the ability to hold his hand close to his face.

The symbolism of getting his new arm this weekend was not lost on him.

When you lose an upper extremity, you lose your independence, your ability to take care of yourself, he said. When you lose your independence, you lose somewhat of your dignity as a human being because you have to depend on others to comb your hair, go to the bathroom. With a prosthetic limb, your independence and dignity are returned to you. This is freedom, let me tell you. When I dont have my arm on, I think I am disabled. But when I have this arm on, I dont think Im disabled.

A version of this article appears in print on July 3, 2017, on Page A15 of the New York edition with the headline: For Two Veterans, a Freedom Restored for Independence Day.

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For Two Veterans, a Freedom Restored for Independence Day - New York Times