Battle at the Triskelion

The Battle at the Triskelion was the battle between HYDRA and S.H.I.E.L.D., and a major event during the HYDRA Uprising. After HYDRA was revealed to be active inside of S.H.I.E.L.D., Nick Fury faked his death and recruited Captain America, Black Widow and Falcon to fight against HYDRA. The Winter Soldier fought alongside HYDRA while he was brainwashed.

Background
After the attack on Nick Fury, Captain America became a fugitive from S.H.I.E.L.D. by order of Alexander Pierce, because Rogers would not give Pierce the USB drive Fury obtained and gave him after the Hijacking of the Lemurian Star.

Black Widow became a fugitive for assisting Rogers and decrypting the USB drive at Camp Lehigh. There she and Rogers learned the secret of S.H.I.E.L.D. from Arnim Zola: HYDRA was a part of the law-enforcement agency.

The two needed an uncompromised ally, so they recruited Sam Wilson, a paratrooper who had access to mechanical wings.

The Winter Soldier, a legend in the espionage community, was really Bucky Barnes, Steve Rogers' best friend, believed killed in World War II.

Pierce invited the World Security Council to Washington, D.C. to witness the launch of Project Insight, a project of S.H.I.E.L.D., corrupted by HYDRA, that would preemptively strike dangerous targets.

Battle
The battle began when Captain America, Falcon and Maria Hill infiltrated the Triskelion's communications room. Rogers then used the intercom to notify all of the workers in the building of HYDRA's plot, urging them to stop the launching of the Helicarriers.

HYDRA agent Brock Rumlow ordered the launch be preempted but the technician refused. Agent Sharon Carter pulled her sidearm on Rumlow who cut her hand with his knife and stole her gun. This resulted in a shoot out with the rebelling S.H.I.E.L.D. agents which Rumlow was able to escape. Rogers and Falcon then boarded the Helicarriers.

Meanwhile, in the World Security Council room, Alexander Pierce's identity had been revealed to the other council members due to Rogers' speech. The council members were even more shocked when agents filled the room and held them all at gun point. Pierce then asked Councilman Singh if he would perform the same method to save his daughter. Singh curtly replied he would not, much to Pierce's amusement. When Pierce prepared to shoot him, Councilwoman Hawley suddenly attacked Pierce and his men, single-handedly taking them all down. She then held a shocked Pierce at gunpoint, and revealed herself to be none other than Black Widow in disguise.

While this was happening, Rogers and Falcon managed to replace the firing chips on two of the Helicarriers. However, on the third carrier, Rogers and Falcon were attacked by the Winter Soldier. Falcon was thrown off the ship and managed to parachute to safety on top of the Triskelion, but his suit was damaged. Rogers however remained on the ship and headed for the control room.

In the Council chamber, Romanoff began to disable the security protecting classified information, and proceeding to dump it on the internet, exposing HYDRA's infiltration to the world. Pierce pointed out that it would also expose S.H.I.E.L.D.'s and Romanoff's dirty business in the process, but Romanoff was undeterred. Pierce then realized that such information required two high ranking members of S.H.I.E.L.D. Right on cue, Nick Fury arrived by helicopter, and confronted Pierce. Pierce attempted to convince Fury that their ambitions were the same, but Fury refused to listen and forced Pierce to deactivate the security.

Rogers then confronted Barnes in the control room. After attempting to persuade Barnes to relent, Rogers then battled him. The two battled back and forth until finally Rogers broke Barnes' shoulder and partially suffocated him. However, while he attempted to replace the chips in the system, Barnes shot him from below.

Pierce then used his phone to activate the tags on the Council members, burning them. Romanoff, having disguised herself as Hawley, was forced to drop her gun due to the tag on her chest.

When the Helicarriers reached 3000 feet, they were ready to kill thousands of targets. Luckily, a wounded Rogers replaced the chips, disabling the control systems in the carriers. This allowed Agent Hill to take control of the Helicarriers, and promptly commanded the ships to fire on each other. The Helicarriers wildly began to destroy each other, with Rogers and Barnes still trapped in one of them.

A disappointed Pierce then intended to make his escape, using Romanoff to fly him to safety. Romanoff then activated a Taser Disk in her hand, which sent a current through her body and disabled the tag on her chest. Romanoff collapsed to the floor, and as Pierce tried to reactivate the tag, Fury picked up a gun and shot Pierce dead.

With Rumlow heading for the Council room, Hill ordered Falcon to head him off. The two got into a fist fight, but their fight was interrupted by one of the falling Helicarriers crashing into the building. Rumlow was buried under the cascade of rubble, but Falcon threw himself through a window and landed in a helicopter piloted by Fury.

In the falling Helicarrier, Rogers removed Barnes from fallen rubble, and attempted to convince Barnes of his identity. A confused and infuriated Barnes assaulted Rogers, but suddenly remembered that they were friends. Rogers then fell from the Helicarrrier and landed in the. However, he was saved from drowning by Barnes, who helped him ashore and vanished from sight. Rogers was later hospitalized, along with Rumlow.

Aftermath
Because of information Black Widow shared across the internet, S.H.I.E.L.D. was labelled a terrorist organization and the international community disavowed any cooperation with it. Congressional hearings were held interrogating various S.H.I.E.L.D. agents that could be found, including Romanoff and Maria Hill. Both managed to avoid imprisonment, with Romanoff declaring that they needed her, and could not afford to lock her up. To this the hearing committee had no answer, and Romanoff was allowed to leave. Maria Hill managed to salvage a job in Stark Industries to protect herself from the FBI. Nick Fury meanwhile continued to live on in secret, with the world still believing him to be dead.

The Winter Soldier went to the Smithsonian Institution where he observed the Howling Commandos display, reflecting that he now has knowledge of his past.

The Hub became one of S.H.I.E.L.D.'s main headquarters because HYDRA failed in its takeover attempt there. Many S.H.I.E.L.D. agents to avoid persecution sought jobs in other parts of the intelligence community, such as Sharon Carter who joined the CIA.

The civilian community partially blamed President Matthew Ellis for the debacle.