The Advanced Threat Containment Unit (ATCU) is a special task force that the U.S. government created to replace S.H.I.E.L.D. Their purpose is to handle any alien threats that arise and contain them. The President gave the A.T.C.U. license to act with any authority deemed necessary.
Rosalind believed the purpose of the A.T.C.U. was to find a cure for terrigenesis and thereby turn inhumans back into humans, but really Malick created the A.T.C.U. as a means of collecting inhumans for Hive to control when he returned to Earth.
All of the inhumans the A.T.C.U. captures are put in gel matrix cubes which are filled with a kind of suspension gel. Rosalnd described it as like putting someone in a medically induced coma until a cure can be found and she assures Coulson that the suspension is for these peoples own good as this way they can't hurt themselves or others.
Gen. Talbot was appointed as the head of the A.T.C.U. after Rosalind is killed.
In "A Wanted (Inhu)man," after Lincoln escapes from a team of A.T.C.U. agents, the A.T.C.U. gives Lincoln's picture and information to every law enforcement agency in the country, referring to Lincoln as an "alien terrorist." In the same episode, Banks is about to capture Daisy, but Coulson convinces Rosalind to let her go by becoming a consultant for the A.T.C.U.
In "Many Heads, One Tale," Bobbi and Hunter pose as F.B.I. agents to get inside an A.T.C.U. facility. While Bobbi searches the facility, Daisy hacks into the A.T.C.U.'s computer network and learns the the A.T.C.U. is requiring all employees to take fish-oil pills that contain terrigen and would cause an inhuman to go through terrigenesis. Furthermore, Bobbi finds a lab marked "enhanced specimen control" where she finds a freezer filled with dozens of boxes containing the cocoon shells of inhumans. Rosalind was led to believe no one was allowed access to that area "for risk of infection."
In "Maveth," Malick has a number of inhumans brought from Endotex Labs to the English castle as this way when Hive comes through the Monolith portal his army will be ready and waiting for him. However, Lash escapes and kills all the other inhumans before Hive arrives.
In "Watchdogs," the Watchdogs implode an A.T.C.U. storage facility; the Watchdogs want to exterminate all powered people and they believe the A.T.C.U. only protects them. However, it's later revealed that the implosion was only to cover up the fact that the Watchdogs stole a warhead from the facility before destroying it.
In "Bouncing Back," the President asks S.H.I.E.L.D. for help in dealing with inhumans, but he also explains that he can’t officially support S.H.I.E.L.D. as many people still view S.H.I.E.L.D. as a terrorist organization. Therefore, the A.T.C.U. will still be the face of the government’s response to advance threats while S.H.I.E.L.D. still continues to protect people secretly. Also, the new head of the A.T.C.U., Gen. Talbot, will being working under Coulson.
- Endotex Labs is the name of the facility where the A.T.C.U. stores all the inhumans they've captured.