What is "englandspiel"

("The England Game"), also called Unternehmen Nordpol (Operation North Pole), was an enormous counter intelligence operation launched by the German intelligence agency, the Abwehr, during World War II. German forces captured Allied resistance agents operating in the Netherlands and used the agents' codes to fool the Allies into continuing to provide the agents with information and supplies. About 50 Allied agents were identified, captured, and executed.