In April 1950, Soviet fighters shot down a US Navy PB4Y-2 Privateer patrol bomber over the Baltic Sea. At the time, Privateers were used by the US Navy for signals intelligence flights off of the coast of the Soviet Union and the People’s Republic of China.
The Soviet Foreign Ministry acknowledged the attack, but stated the aircraft was flying in Soviet airspace, and had fired on Soviet fighters when they attempted to signal it to land. The Soviet government also stated it had no information about survivors from this flight.
American search and rescue efforts were unsuccessful, but two unmanned life rafts and some wreckage were eventually recovered.
The United States maintained that the crew members were captured and held in Soviet Gulags until their death. The Soviets denied this.
Source: Remembering Crew Members of U.S. Navy PB4Y-2 Shoot Down, April 8, 1950 – And Shocking Cold War Case Study – Station HYPO