The Office of the Under Secretary of Defense for Intelligence and Security, known as OUSD(I&S), is the staff of the Pentagon's senior civilian intelligence official. Congress created the post of Under Secretary of Defense for Intelligence in the defense authorization act for fiscal 2003, and Stephen Cambone took office in March 2003; the fiscal 2020 act added "and Security" to the title. The under secretary advises the secretary and deputy secretary on intelligence, counterintelligence and security, oversees the Defense Intelligence Agency, the National Security Agency, the National Geospatial-Intelligence Agency, the National Reconnaissance Office and the Defense Counterintelligence and Security Agency, and also serves as Director of Defense Intelligence under the Director of National Intelligence. Holders have included James Clapper from 2007 to 2010 and Ronald Moultrie from 2021 to 2024, and Bradley Hansell took office in July 2025. Since the department adopted "Department of War" as a secondary name in September 2025, the office also appears as the Office of the Under Secretary of War for Intelligence and Security.

The office first enters the UAP record through the Advanced Aerospace Threat Identification Program. According to the All-domain Anomaly Resolution Office's 2024 historical report, the Defense Intelligence Agency set up the related AAWSAP contract in 2009 "in coordination with" the office, and when Senator Harry Reid asked that year for the effort to become a special access program, Deputy Secretary William Lynn declined on the recommendation of Clapper, then under secretary. The same report says AATIP was never an official program and that, after the contract ended in 2012, the name was used by an informal community of interest with no dedicated staff or budget. Luis Elizondo, who worked in the office until resigning in October 2017, has said he directed AATIP from there, while a Pentagon spokesman said in 2019 that Elizondo had no AATIP responsibilities during his time in the office.

Its formal UAP role began in August 2020, when Deputy Secretary David Norquist approved the UAP Task Force, led by the Navy under the office's cognizance. In November 2021 Deputy Secretary Kathleen Hicks directed the under secretary to establish the Airborne Object Identification and Management Synchronization Group to succeed the task force, and in July 2022, after the fiscal 2022 defense act, that group was renamed the All-domain Anomaly Resolution Office and given a wider mission. Under the statute, AARO's director reports directly to the deputy secretary of defense and the principal deputy director of national intelligence on operational and security matters, and to the under secretary on all administrative matters.

That lineage drew criticism in May 2026, when the journalist Christopher Sharp argued that whistleblowers' distrust of AARO was sharpened by its origin inside an office whose responsibilities include intelligence, counterintelligence, security and insider-threat policy. He cited a 2025 special access program security manual under which the office "establishes, develops, and coordinates DoD SAP security policy."

The office has moved from a contested coordinating role in an intelligence contract to serving as the administrative parent of the department's official UAP organisation, and every Pentagon UAP office since 2020 has been created under its cognizance or administered through it.