Captain America is rarely without his iconic vibranium shield. No matter where he goes or what he does, Steve Rogers is always ready to throw his trusty shield at a moment's notice. For a time, however, this character-defining tool was replaced by a new shield of pure energy.
This new shield was originally developed from technology used by the Raiders, criminals who appeared in Iron Man #145, by David Micheline, Bob Layton and John Romita Jr. Tony Stark repurposed this shield of photon energy to supplement his own armor's shielding. This way, Iron Man could be protected from even the most extreme attacks. Years later, Captain America used a new version of this energy shield in Captain America #451, by Mark Waid and Ron Garney. During this time, Steve Rogers was stripped of his shield and US citizenship by the president, as he had been seen working alongside the Red Skull. Of course, this was merely temporary, and Steve returned to his old shield as soon as he was welcomed back into the US.
Related: Captain America’s Secret Avengers Saved the World by Blowing Up a City
It wasn't until Captain America #2, by Waid and Garney, that The Sentinel of Liberty desperately needed a new shield. After rescuing a Navy submarine from HYDRA, Steve lost his original shield at the bottom of the ocean. Captain America had people scouring the ocean for his lost shield, but in the meantime, he needed a replacement. For a brief period, The Star-Spangled Avenger adopted a replica of his original triangular shield. Steve used this classic shield until it was damaged during the events of "Live Kree or Die." In Captain America #9, by Waid and Andy Kubert, the energy shield made its return. Sharon Carter bestowed this new model, developed by SHIELD, upon The Sentinel of Liberty. This formidable weapon could be contained within a small unit on Steve's wristband, making it easily accessible.
The photon energy from this wristband could morph into many forms, including a staff, sword, rope and of course, Steve's original shield, sporting the red, white, and blue. Another handy feature was the ability to shoot beams of pure energy from the wristband. With this new shield, Captain America fought foes like AIM and the Red Skull, before finally recovering his old shield. In Captain America #21, by Waid and Kubert, Tony Stark found Steve's shield, although seemingly broken beyond repair.
Apparently, there was a flaw in the shield's molecular structure. With each strike to the shield, the flaw spread, as a sort of "vibranium cancer" which would destroy the weapon. Not only would the shield be destroyed, but its deadly vibrations would spread to all of the vibranium around the world, cumulating in several explosions. The most dangerous explosion would come from Wakanda's vibranium mound, in a blast which could destroy the world.
Setting out for Wakanda, Captain America hoped to use his broken shield to absorb the vibranum mound's shockwaves, saving the world and sacrificing his shield. Yet the villainous Klaw arrived first, absorbing the vibranium's vibrations into his own body and converting them to sound. The Star-Spangled Avenger used his shield to absorb the sound, and, luckily, the harmonics restored the nanostructure of Steve's shield. The energy shield, meanwhile, lived on in the future. Indeed, when Captain America and Michael Korvac went into the 31st century, Korvac and Steve fought for a long period of time. Every time Steve rebelled against Korvac's rule over this future, Korvac killed him and reset time.
The only person outside of this time loop was Korvac's servant, Primax. Witnessing Captain America's bravery, Primax was inspired to turn against his master, using the energy shield. This act of courage allowed Primax to remember his real name: Jaromel. Once Captain America and Korvac returned to their original time, Jaromel fought on as the future's Captain America, wielding the energy shield. Steve Rogers' energy shield may have only been temporary for him, but it shall be used for generations in the distant future.