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Fireteam Crimson is a team of Spartan-IV supersoldiers. Crimson was assigned to UNSC Infinity during the ship's second expedition to the Forerunner shield world Requiem in February 2558. Operating on Requiem, Crimson is frequently assigned on ground missions in which they combat the shield world's resident Promethean constructs and Jul 'Mdama's Covenant faction.
- Unidentified Spartan-IV Mark VI Mod
- Unidentified Spartan-IV Enforcer
- Unidentified Spartan-IV Orbital
- Unidentified Spartan-IV Recruit
- Unidentified Spartan-IV Scout
In 2558 Crimson was deployed in a joint UNSC military operation on Requiem alongside Fireteams Castle, Majestic, Domino, and Ivy. Spartan Jared Miller was personally assigned to Crimson as their mission handler. Crimson was dropped behind-enemy-lines to assist marines in neutralizing Covenant forces in the area. In an attempt to stop the Covenant from establishing permanent bases throughout Requiem, Crimson was also given the objective to destroy four power cores acting as short-range wireless transceivers, and was successful. After mopping up whatever Covenant forces were left in the area, Miller sent a Pelican dropship for extraction. Commander Sarah Palmer congratulated them on their mission success.
Subsequently Crimson was sent to capture a Covenant-held power station on Requiem, Sniper Alley. They were tasked with eliminating all Covenant forces within the area. Miller concluded that the Covenant were siphoning large amounts of energy from a nearby Forerunner structure. Spartan Robert Dalton came online and readied an orbital-strike from the Infinity to destroy the target energy source. The target was destroyed by Infinity, and Fireteam Crimson was extracted from the area. Crimson and Majestic were sent north of the UNSC's area of operations in Requiem in order to shut down Forerunner power generators at the Fortress. Both teams were sent to their individual locations to complete their objectives. Upon insertion, both Crimson and Majestic had their long-range communications jammed, but deactivated the jammers. The area was quickly swarmed with Promethean Crawlers and Promethean Watchers as Crimson fought to disable the arrays powering the Forerunner structure. Initiated by Palmer, the mission turned into a competition where both fireteams were trying to complete their mission objectives first. Majestic temporarily took the lead, but Crimson eventually beat Majestic. Dalton arrived in a Pelican dropship for Crimson's extraction.
Next Crimson was sent to The Refuge, a jungle Forerunner structure that scientists were preparing to set up shop in. They were attacked by more Promethean forces and activated a star chart. Miller processed the data and Palmer tried to get them extracted. The door locked, shutting Crimson in the facility, and Promethean Knights arrived in the area. Crimson beat off the foes while Miller opened the door allowing Crimson to escape on Dalton's Pelican.  Crimson was then sent into a Covenant dig site at The Cauldron, a Forerunner area. The Covenant resistance was strong, leading Palmer to wonder what they were guarding. Crimson fought their way to a mysterious artifact guarded by Promethean Knights. After fighting them off, Crimson recovered the Artifact, boarded the Pelican, and brought it back on Infinity. 
Later Crimson was sent in to the Gate, a location that the Marines had failed to take from the Covenant. After fighting through Kig-Yar and Unggoy they faced Promethean resistance. The incoming Prometheans were dispatched by Crimson, and Miller tasked the team with disabling pylons controlling Forerunner turrets. Dalton came in and evacuated Crimson after they faced more translocating Knights and Crawlers. They were sent to respond to a Science Team's Distress Call. . The aforementioned science team hid behind a forcefield when the Covenant attacked, and were the science team assigned to the Cauldron. Crimson destroyed Covenant communications arrays, and found beacons and IFF tags from the science team. Dr. Morgan Rivera was brought on comms who gave Crimson her location. Crimson fought through the Covenant and rescued her and her team. 
Next Crimson was sent in to evacuate Marine squad Hacksaw who was attacked by Covenant at the Fortress. They were dropped in and beat back waves of Covenant forces to rescue the Marines. The group moved to the top of the Fortress to be evacuated by Dalton, but Phantoms arrived carrying Sangheili Warriors and Sangheili Zealots. Crimson destroyed the Phantoms and Sangheili and were evacuated. En route to the Refuge, Crimson was shot down in Sniper Alley by nearby anti-air turrets and were thought to have died. Miller learned that Fireteam Crimson was still alive and they were sent to take out the turrets. Covenant forces arrived supplanted by Heavy orbital insertion pods, but Crimson eliminated the Covenant and the turrets and continued with their mission. Reaching the Refuge, Crimson saw no sign of Gagarin team, the science team based there. They learned Gagarin activated Forerunner artifacts, and Crimson deactivated them under resistance from Promethean forces. They got on a Pelican and left, not having found Gagarin team.
Hunting a terrorist
Commander Palmer deployed Crimson team to a rocky area of Requiem to hunt for Parg Vol, a Sangheili terrorist and associate of Jul 'Mdama. After facing heavy Covenant resistance, they were unable to kill Vol and he escaped. Crimson was then sent to Galileo Base, a science facility on Requiem under heavy attack by Covenant forces. They managed to beat back the Covenant and drive them away from Galileo Base. Next Crimson arrived at Two Giants, a canyon with two Beam emitters, to assist Spartan squad Mountain. Beating off Covenant forces Crimson retrieved the marines and activated Forerunner technology in the towers. The Covenant responded by sending an entire fleet of foes from a CRS-class light cruiser. Palmer dropped in several Mantis mech suits which Crimson used to beat back the fleet while the cruiser was destroyed.  Vol was once again located, this time re-taking the Gate location with his Covenant forces. Crimson neutralized him and several Covenant and Promethean warriors. 
Chasing Jul 'Mdama
Soon after, Crimson was then sent to disable a Covenant communications array at the site the Covenant had previously had anti-air turrets. The array had led to the death of Fireteam Castle, and Crimson rushed the location and tapped into the array before disabling it.  UNSC Infinity found data possibly leading to Jul 'Mdama's location. The data placed 'Mdama at the Two Giants location where a tower had been retaken by Covenant forces. Activating Forerunner technology, a portal opened and Crimson stepped through.  They emerged in the Fortress location and re-established communications primarily with the AI Roland. After fighting off enemy forces Crimson steped through another portal, chasing 'Mdama.  Crimson emerged in the middle of Covenant enemies at the Cauldron, and fought through them to reach 'Mdama. Infinity bombed 'Mdama's location causing him to drop the Didact's Gift, which was recovered by the UNSC and subsequently brought to Galileo Base.  However, the Covenant attacked Galileo Base with the intent of recovering the gift. Crimson beat them back and activated the base's defense systems, holding back the Covenant but Prometheans translocated in the base. Crimson fought them off and left Fireteam Majestic to take the gift to Infinity. 
On Crimson's next deployment, they were sent to the Gate to investigate Dr. Leslie Boyd's power fluctuations back at the Refuge with only Roland and Miller to help them. They were being caused by translocating Prometheans, and they were at risk of destroying Boyd's power generators. They defended them from raids of Prometheans until Boyd could finish his work and block their translocations. Boyd opened a portal for Crimson, now able to control the portal's locations.  At the Refuge the science base came under attack by Prometheans, which were driven off by Crimson.  A battlecruiser began sending a Covenant army down to the Refuge, and Crimson defended the location while Fireteam Shadow took out the cruiser. Successfully defending Dr. Boyd, Crimson team left on a Pelican to their next objective.  Crimson arrived at Forward Base Magma to defend power generators from Covenant forces. After doing so, Roland found Gabriel Thorne's IFF tag in the area, and found it alone with signs of a struggle.  Crimson was dropped off in an area with Covenant forces to try and find Thorne. Despite defeating a large amount of Covenant, Thorne was not found. A Pelican arrived for evac but was destroyed by the Covenant. Phantoms and Banshees then converged on Crimson's position, along with a single light cruiser. 
Capture and escape
Fireteam Crimson was eventually captured and brought to a Covenant detention facility. After Roland located Crimson, Miller ordered a diversionary bombardment by Dalton. The resulting explosion distracted the guards, which allowed Crimson to escape. Crimson then neutralized the remaining guards and fended off waves of reinforcements as they attempted to escape. They deactivated a shield door and engaged more Covenant including Shade turrets. Miller decided Crimson must hijack a Phantom to escape, however after entering the next area a Marine squad known as Icebreaker was detected. Crimson engaged the guards, which included Promethean Crawlers. After freeing the Marines, one of them, Lieutenant TJ Murphy, said he could remotely take over a nearby Phantom. Crimson covered him while he did so, holding off several waves of Covenant troops. Eventually Lieutenant Murphy was able to take over the Phantom, allowing Crimson and the surviving Marines to escape.
Fireteam Crimson used their captured Phantom to great use. They first infiltrated a secure Covenant facility and retrieved vital intelligence from the computers there. This led them to a central intel facility based in the Warrens. Crimson attacked the facility and gained access to a Covenant computer, which revealed the locations of a Covenant archaeological dig and a plasma supply depot. Crimson was sent to destroy the supply depot, while Fireteam Switchback was sent to stop the dig.
Crimson successfully infiltrated the supply depot and destroyed the plasma stockpiles. However, they also discovered that the Covenant had stolen a large amount of UNSC weaponry - including nuclear weapons. The warheads themselves could not be found. They then received a distress call from Switchback, who were at the dig site. Crimson headed over to the dig site to help Switchback, but discovered no trace of the team except for their IFF tags. On Commander Palmer's orders, Crimson attacked and disabled the Harvester the Covenant were using in their dig.
Defending the Infinity
Later, when the Infinity came under attack by Covenant and Promethean forces, Crimson was recalled to help defend the ship. Because Crimson was already engaged in an operation at Apex when the Infinity was attacked, Crimson had to clear the area of enemy forces in order to let Murphy pick them up. Murphy assisted by delivering Crimson a Mantis, which greatly aided in clearing out Apex. Murphy then picked Crimson up in his Phantom and took them back to Infinity.
On their way back to Infinity, Crimson's stolen Phantom was damaged by the ship's own automated defenses. They crashed into a hangar bay, but survived. After clearing out the initial Covenant boarders inside the hangar, Crimson tried to seal the hangar doors to block off further intrusions in that area. However, the door controls malfunctioned due to the effects of the Artifact. Roland instructed Crimson to head to the server room and power cycle the systems there. Crimson did so, and restored hangar controls. They then fought their way back to the hangar and closed the doors again.
Crimson then had to face another crisis: The Covenant had broken into the engine room and were planning to destroy the ship with the stolen nuclear warheads. After a quick detour to the server room - where they stopped the Covenant from detonating one of their nukes - Crimson entered the engine room. They cleared out the initial Covenant intruders and disarmed all the warheads. A new wave of Covenant soon attacked the engine room, but Crimson successfully repelled them. They then sealed off the engine room by closing the emergency bulkhead doors.
At that point, the Covenant disabled Infinity's aft weapons. On Miller's orders, Crimson headed over to aft weapons control, where they destroyed the Covenant's hardware jamming devices preventing the guns from firing. They then brought the ship's weapons back online. Crimson was then ordered to retake the server room, which had again been invaded by enemy forces. They secured the server room for a third and final time, then returned to the hangar bay. There, they battled and defeated a large force of Hunters. By now, the tide had turned in the UNSC's favor.
Return to Requiem
After Infinity was secured, Crimson was redeployed to Requiem, where they performed a number of operations. They first retook Apex from the Covenant and shut down several portals. They then destroyed Covenant artillery batteries besieging Fireteam Majestic. They then aided Fireteam Lancer in destroying a Covenant base hidden in the Warrens. During this mission, they found and rescued the survivors of Fireteam Switchback. During these operations, Miller noted that the Covenant seemed to be able to predict their moves. After Miller and Palmer learned about a Covenant listening post from a captured Elite, Crimson was sent to the outpost to investigate. There, they discovered a captured UNSC Pelican being used to listen in on the UNSC's communications. Crimson cleared the Covenant defenders and Infinity launched an aerial bombardment that destroyed the Pelican.
Dr. Glassman then requested Crimson's aid in deciphering a holographic map of Requiem. To this end, Crimson attacked a Covenant base located at a specific Forerunner structure. Glassman was able to use the map to guide Crimson in activating the structure's automated defense systems, which easily destroyed Covenant reinforcements.
Searching for Halsey
After Catherine Halsey's abduction by Covenant forces, all Spartan fireteams were dispatched to find her. Fireteam Crimson was first sent to a location on Cyclone where they investigated a transmission seemingly sent by Halsey. After clearing out the Covenant forces guarding the base, they delved deeper into the structure and found a Covenant comm terminal with a message from Jul 'Mdama, ordering all forces to head to Librarian's Rest. While investigating, Crimson came under attack by Prometheans. The Spartans were unexpectedly aided by Sentinels under the control of the Librarian. Roland eventually traced Halsey's transmission to another Covenant-occupied Forerunner structure. Upon investigating, Crimson learned the transmission had been sent to Lockup. Crimson then investigated another transmission sent by Halsey through Apex this time. Using Scorpion Tanks, the Spartans fought their way through Covenant and Promethean forces and reached the terminal where Halsey's transmission had been sent to. This transmission had also been relayed to Lockup.
Upon being deployed at Lockup, Crimson stormed the facility and defeated the Covenant guards. However, Covenant and Promethean reinforcements soon showed up, forcing them not only to fend for themselves, but also assist the Marine squad that had accompanied them. After repelling the attackers, Crimson found a grav lift that led them to the top of the structure. There they discovered that the Covenant had previously (and unsuccessfully) tried to force a captured Marine squad to activate a Forerunner device. Crimson defeated a final counterattack by Covenant forces, then activated the device themselves. The device revealed holographic map of Requiem similar to the one Dr. Glassman had found earlier. Roland determined they could use this map to find a way to free Infinity from Requiem.
During the final phase of the Second Battle of Requiem, Fireteam Crimson was dispatched to locate and disable one of two Forerunner artifacts on Requiem that were binding Infinity to Requiem. Their task was made all the more urgent when Jul 'Mdama sent Requiem on a course with the sun.
Following the coordinates Dr. Glassman had derived from the map, Crimson returned to the dig site. There they discovered that the Covenant itself had been after the artifact, which was buried deep within the mountain. Miller ordered them to recapture the Harvester they'd previously disabled, and use its plasma drill to breach the rocks. The Harvester was shielded and air support was needed to disable it. After Crimson destroyed three Forerunner anti-aircraft guns guarding the area, Murphy arrived in a Pelican and disabled the Harvester's shield. Crimson then boarded the Harvester and eliminated the Covenant crew. They also rescued some captured scientists who the Covenant were forcing to fix the Harvester. Unfortunately, the Harvester's power supply had been destroyed by Crimson during their previous raid. Roland came up with a plan to find a new power source located at Apex.
Due to heavy enemy activity at Apex, Crimson was unable to go there directly. Instead, they landed at the Warrens and took a back route to Apex through a Covenant base. Once at Apex, Crimson joined forces with Fireteam Forest, a Spartan Fireteam that had been trapped on Apex earlier. Crimson and Forest fought their way to a Covenant communications terminal, and, on Roland's orders, activated it. This summoned a Lich to the scene. Roland explained his plan for Crimson to board the Lich and steal its power core. Despite the numerous waves of troops the Lich sent at them, Crimson boarded the ship, eliminated its crew, and stole the engine core. They then returned to the Warrens, where they disabled the power source for the Forerunner AA guns in the area. They then used a salvaged Mantis to fight their way back outside, where they were picked up by a Pelican.
Crimson recaptured the Harvester and powered it back up using the Lich's engine core. They used the Harvester's plasma drill to carve out an entrance in the rocks, exposing a cave. Crimson entered the cave and fought their way through numerous Prometheans before finally reaching the artifact, which was housed within a massive Forerunner structure. They deactivated the artifact and escaped as the cavern began to collapse. Near the exit, Crimson encountered one last group of Sangheili. After defeating the Elites, Crimson exited the cave and made it back outside, where Murphy arrived in a Pelican to pick them up.
Shortly afterwards, Commander Palmer and Fireteam Majestic located and disabled the second artifact. They too left Requiem in a Pelican. Crimson and Majestic made it back to the Infinity just in time to escape Requiem's destruction.
- Fireteam Crimson are the playable protagonists of Halo 4's Spartan Ops cooperative campaign. Like Noble Six in Halo: Reach, their appearance, gender, and equipment are determined by the players. Even the size of the team is not established in the game, as *Spartan Ops supports between one and four players per chapter. Presumably Crimson has four members, though, as that is the recommended team composition for Spartan Ops sessions (as well as the default team size in matchmaking). Nonetheless, dialog and the Fireteam designation clearly indicate that Crimson canonically has multiple members.
- A set of MegaBloks is specifically dedicated to Fireteam Crimson. It includes five Spartan-IVs clad in red Recruit, Mark VI, Orbital, Enforcer and Scout armors. As MegaBloks is accorded a certain degree of artistic freedom, it is unlikely that they necessarily represent the canonical appearance of Fireteam Crimson.
- Crimson's only role outside of Spartan Ops is a mission called "CHATTERBOX" in the Infinity Briefing Packet's Mission Briefings that apparently they took part in.
- The Halo 4 downloadable content Crimson Map Pack is named after Fireteam Crimson.