Which unit operates under national security interests within immigration?

The National Security Branch is the correct answer because it functions specifically within the context of immigration to ensure that national security interests are prioritized. This branch is tasked with integrating national security strategies into immigration policies and enforcement. Its role includes monitoring, assessing, and managing potential threats that may arise from immigration processes, thereby safeguarding the nation while ensuring the integrity of the immigration system.

Other units mentioned, while they may have roles related to security and surveillance, do not specifically focus on managing immigration in relation to national security. The National Security Bureau and the National Surveillance Unit are not recognized entities within the context of U.S. immigration law as it pertains to direct immigration operations. The National Security Agency, although it plays a critical role in safeguarding national security on a broader spectrum, is primarily focused on intelligence and communications rather than directly managing immigration matters. Thus, the National Security Branch is distinct and directly relevant to the immigration context within which national security interests are operated.