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Soviet aircraft shot down a Swedish military plane carrying out signals-intelligence gathering operations, followed three days later by the shootdown of a second plane searching for the first one.

Historical image related to Soviet aircraft shot down a Swedish military plane carrying out signals-intelligence gathering operations, followed three days later by the shootdown of a second plane searching for the first one. from June 13, 1952

Catalina affair

1952 Cold War–era diplomatic crisis

The Catalina affair was a military confrontation and Cold War-era diplomatic crisis in June 1952, in which Soviet Air Force fighter jets shot down two Swedish aircraft over international waters in the Baltic Sea.
Source: Wikipedia (CC BY-SA)

Signals intelligence

Intelligence-gathering by interception of signals

Signals intelligence (SIGINT) is the act and field of intelligence-gathering by interception of signals, whether communications between people or from electronic signals not directly used in communication. As classified and sensitive information is usually encrypted, signals…
Source: Wikipedia (CC BY-SA)