Linked from

The 19 pages that link to Signals intelligence, each with the reason it gives.

• SurveillanceRelated: It monitors communications rather than relying on direct visual observation.

• Electronic warfareRelated: Electronic-support collection can contribute to intelligence about adversary systems and activity.

• Aerial reconnaissanceRelated: Airborne platforms can collect radio emissions as well as images of physical targets.

• EspionageBroader topic: Electronic interception can reveal secrets without placing an agent inside an organization.

• Mass surveillanceNarrower topic: Its interception methods and infrastructure underpin many state surveillance capabilities.

• Human intelligenceCompared with: It collects through transmissions and sensors rather than human reporting.

• National Security AgencyNarrower topic: The NSA’s foreign collection mission is a major part of this broader intelligence discipline.

• UltraNarrower topic: Ultra became one of the best-known achievements in the broader field of signals intelligence.

• Drone warfareRelated: Some military drones carry equipment for collecting electronic emissions.

• Information warfareRelated: Intercepted signals can reveal an adversary’s plans while exposing vulnerabilities in its communications.

• Open-source intelligenceCompared with: SIGINT generally depends on access to signals that are not publicly available.

• Gulf of Tonkin incidentRelated: Intercepted communications were cited as evidence of a North Vietnamese attack on August 4.

• DefectionCompared with: A defector may reveal context that intercepted signals alone cannot supply.

• J. E. B. StuartRelated: Union signal stations sometimes exposed Confederate movements that Stuart’s cavalry sought to conceal.

• Reconnaissance aircraftRelated: Specialized aircraft collect transmissions that imagery sensors cannot reveal.

• Military intelligenceBroader topic: It is one collection discipline used to learn about adversaries.

• Electronic warfare aircraftNarrower topic: It is the broader intelligence discipline that includes electronic intelligence relevant to these aircraft.

• Surveillance aircraftNarrower topic: Some aircraft collect radio emissions rather than relying on images of the ground.

• Hideo IwakuroRelated: It was one source of evidence used to estimate foreign military capabilities.