1960 RB-47 shootdown incident
On 1 July 1960, a United States RB-47H reconnaissance plane was shot down by the Soviet Air Defence Forces while performing signals intelligence in the Barents Sea, near the Kola Peninsula, off the Arctic coast of the Soviet Union. Four of the six crew members died.
Source: Wikipedia — 1960 RB-47 shootdown incident (CC BY-SA 4.0)