The Multiple Threat Asessment Center, commonly known as MTAC is used to provide warnings about a wide range of threats to the Navy and Marine Corps. It is operated by NCIS, with staff on hand 24 hours a day.
In the series, Gibbs and his team regularly go to MTAC if they want to keep tabs on a suspect or have a conference call. Different techs are stationed in MTAC around the clock to help keep track of the communications going through the center and to also bring any incoming satellite or conference calls online, some of which are from other personnel or other agents agencies.
For possible security reasons, an iris scanner is at the entrance. It allows various Directors and Agents to gain access to the room by having their eyes automatically scanned which in turn unlocks the door.