title: Development history of Silverstone Circuit
context: Silverstone Circuit is built on the site of a World War II Royal Air Force bomber station, RAF Silverstone, which opened in 1943. The airfield's three runways, in classic WWII triangle format, lie within the outline of the present track. Since its first use in the 1940s, the circuit has undergone several changes.
question: When was the Silverstone Circuit built?
answers: 1943