Winter Soldier's Prosthetic Arm

"He's fast. Strong. Had a metal arm."

- Captain America about the Winter Soldier

The Winter Soldier's Prosthetic Arm is a cybernetic implant attached to the Winter Soldier's missing left arm.

History
Following James Barnes' fall from Arnim Zola's speeding train, he suffered injuries that included the loss of his left arm. The Prosthetic Arm was only a portion of the reconstruction efforts HYDRA used in turning Barnes into their deadly assassin. The construction of the arm presumably took place in secret HYDRA facilities in the Soviet Union following World War II. With the communist red star imprinted on the arm, the brainwashed Barnes eventually became known as the Winter Soldier.

During his fight with Captain America in Washington D.C. following his attempt to kill Nick Fury, the Winter Soldier's arm was damaged by Captain America's Shield. The arm, which was revealed to be at least partially mechanical, was repaired later by HYDRA doctors in a secret location run by Alexander Pierce.

Capabilities
The arm grants superhuman strength, as it hums very loudly before the Winter Soldier unleashes devestating blows such as causing Captain America to stagger back from a hit on his shield, which is supposed to absorb all vibrations.