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.

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.

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 intelligence may necessarily involve cryptanalysis. Traffic analysis—the study of who is signaling to whom and in what quantity—is also used to integrate information, and it may complement cryptanalysis.