Switzerland's redoubt strategy during World War II was essentially one of deterrence. The idea was to make clear to Germany that an invasion would have a high cost. Simultaneously, economic concessions were made to Germany in the hope that the overall cost of a German invasion would be perceived to be higher than the potential benefits. However, it is clear that Hitler intended to invade eventually and that the Allied landing at Normandy and the difficulties faced in invading the Soviet Union were pivotal in merely delaying an invasion. Concessions included a national blackout and the destruction of a secret German radar system that had accidentally landed in Switzerland in exchange for a dozen aircraft.