No! No! That's just a prototype."
"What's it made of?"
"Vibranium. It's stronger than steel and a third of the weight. It's completely vibration absorbent."
"How come it's not a standard issue?"
"That's the rarest metal on Earth. What you're holding there, that's all we've got.
The second shield used by Captain America was a prototype made from the only supply of Vibranium that the United States Armed Forces had available. Howard Stark presented the shield to Captain America to use as a tool to protect himself from gunfire. It was then integrated into the patriotic motif of Rogers’ uniform, adding a white star to the center and making the three concentric outer circles into red and white stripes.
Captain America carried the shield during all of his raids on HYDRA facilities and other missions during the war. As Rogers chased the Red Skull, the shield took a direct hit from the HYDRA leader's energy-based weapon, saving Rogers from disintegration. Rogers carried the shield with him on his final mission, when he was forced to crash the Valkyrie into the icy waters of the North Atlantic, leaving both Rogers and the shield encased in ice. Almost seventy years later, S.H.I.E.L.D. agents stumbled across the crash site of the Valkyrie. Captain America was found alive, and he and the shield were taken to New York City.
The revived Captain America was asked to join the Avengers, where he again relied on his shield as his primary weapon. On a mission in Germany to capture Loki, he saved an elderly civilian by blocking a shot fired from Loki's Scepter. The shield also saved Rogers' life when it protected him from an attack from a confused Thor, whose attack was deflected, destroying a large area of the surrounding forest. Captain America relied on his shield once again during the Chitauri attack on New York City.
Agent of S.H.I.E.L.D.
In the two years after the Avengers parted ways, Steve Rogers became a full time S.H.I.E.L.D. operative, receiving advanced combat training and field experience that allowed him to learn to more effectively use his shield as an offensive weapon in combat. While performing a number of stealth missions alongside the subdivision STRIKE, the shield was repainted, replacing the red stripes with light blue stripes to make it less conspicuous.
To escape the Triskelion, where he was attacked by STRIKE in an elevator, he made a leap of over twenty stories to escape, landing on his shield, to break his fall.
In the events leading up to the HYDRA Uprising, Captain Rogers had several run-ins with the assassin known as the Winter Soldier, who, unlike others, was able to block Rogers' shield by catching it using his bionic left arm. During one fight with the Winter Soldier, Steve learned of his true identity as Bucky Barnes, Rogers' best friend that he believed had died during World War II. Because of this, Captain America later refused to continue fighting Bucky after completing his mission to disable the three HYDRA controlled Helicarriers, instead allowing his shield to fall from the Helicarrier.
Later, the shield was recovered and left next to Captain America's bedside in the hospital.
I'm always picking up after you boys!
Captain America and Thor used the shield and Mjølnir in tandem during their fights against Ultron Sentries. Rogers would toss the shield into the air and allow Thor to hit it with his hammer to increase its speed as a projectile weapon.
During Rogers' fight with Ultron in the Battle of Seoul, the shield got stuck in Ultron's body and Rogers lost the shield in the street. Black Widow, pursuing the combatants on a motorcycle, noticed the shield on the ground, scooped it up, and returned it to Captain America. The shield saved Rogers from flying debris that came through the windshield of the train as he ordered Scarlet Witch to use her powers to stop its movement. 
Captain America's original shield was a heater-shaped shield that was made of a relatively sturdy metal that allowed Captain Rogers to rely on it as a viable weapon in battle. The outer surface of the shield was painted in an American Flag motif, with an area of blue with three white stars across the top, and a series of vertical red and white stripes running down to the point. The inner surface had the appearance of a polished brass plate and had mounted leather handles that allowed it to be held. This shield was mostly used as a melee weapon to attack enemies directly and provide some protection from gunfire and debris from explosions.
After entering World War II as a fully recognized soldier, Captain America switched to a special, discus-shaped shield made of Vibranium provided to him by the Strategic Scientific Reserve. This shield appeared to be composed of four concentric sections, with fittings on the inner surface for two leather straps that allow the shield to easily be held and worn on Captain Rogers' arm, the straps would later be replaced by an electromagnet worn at the hand.
Captain America relied heavily on the shield as a weapon that was balanced in both defensive and offensive capabilities. Made out of Vibranium, it is able to absorb kinetic energy, enabling it to withstand impacts that would break a shield made of any other material. It was also discovered to be incredibly effective at deflecting or diffusing attacks from energy based firearms such as those developed by HYDRA or the guns used by the Chitauri. It is also shown that it can be used to cushion falls from great heights.
As an offensive weapon, the shield’s discus shape and Vibranium composition make it powerful as both a close-quarters melee weapon and a thrown weapon. In the hands of a trained fighter like Captain America, the shield is a strong melee weapon, using the flat surface and blunt outer edge of the shield to strike enemies in vital areas. In the right hands, the shield is also an exceptional ranged weapon as its Vibranium composition and broad, curved shape allow it to easily move through the air when thrown while maintaining nearly constant velocity and momentum. One of the most unique attributes of the shield is its ability to ricochet after striking a solid surface when thrown, losing very little of its momentum, allowing it to strike several targets, and, if aimed properly, return to the thrower.
The shield originally had a reflective, shiny grey appearance due to its Vibranium composition. However, the shield was later painted to match the appearance of Captain America’s uniform, placing a white star in the center, surrounded by blue, and making the three outer rings into red and white stripes. During modern stealth missions the red sections of the shield would temporarily be covered with a light blue color to make it appear less conspicuous.
|Appearances for Captain America's Shield|
- Prior to making the shield his primary weapon, Rogers showed an affinity for using shields when he fought, such as picking up a circular garbage can lid to protect himself and later ripping off a car door to protect himself from gunfire. He later remarked that he thought of them as useful tools.
- A replica/prototype of the shield can be seen in Tony Stark's workshop in Iron Man and Iron Man 2, first behind Tony when he is first seen removing his armor, and then when he is building a particle accelerator.
- In Iron Man 3, the Mandarin has a tattoo of the shield on his neck. It has been noted that in place of the star is an "A", the symbol for anarchy. Kevin Feige has said that the Mandarin uses "symbolism of various cultures and iconography that he perverts for his own end." A popular theory is that he is attempting to twist the ideals the shield represents. This fits in with the speech that he gives in the trailer.
- In the comic books, the circular shield is made from a unique mix of Vibranium and an iron alloy; attempts to duplicate this mixture led to the development of the more famous but less durable (but still near-indestructible) metal alloy Adamantium. However, the film rights to Adamantium and its origins are held by 20th Century Fox, leading to the production decision to make Captain America's Shield purely out of Vibranium in the Marvel Cinematic Universe.