Dover was a town in England. It was known for its chalk cliffs.
In May 1940, the Tenth Doctor and Donna Noble, near the Dover cliffs in the UK, worked to prevent a Nemonite invasion from derailing a Second World War counterattack called Operation Dynamo. (AUDIO: The Nemonite Invasion)
In 1942, the Third Doctor and Professor Pierre Vedrun tricked Captain Ernst Wolfgang Spiegal into transporting themselves into the inside of a jail cell in a Dover police station. Thirty years later, a police sergeant recalled the incident when the Doctor inquired about it. (COMIC: Timebenders)