high. During an invasion, the Swiss Army would cede control of the economic heartland and population centres but retain control of crucial rail links and passes in the National Redoubt. Switzerland was a base for espionage by both sides in the conflict and often mediated communications between the Axis and Allied powers by serving as a protecting power. In 1942, the United States Office of Strategic Services (OSS) was established in Bern. Through the efforts of Allen Dulles, the first US intelligence service in Western Europe was created. During the allied invasion of Italy, the OSS in Switzerland guided tactical efforts for the take-over of Salerno and the islands of Corsica and Sardinia. Despite the public and political attitudes in Switzerland, some higher-ranking officers within the Swiss Army had pro-Nazi sympathies: notably Colonel Arthur Fonjallaz and Colonel Eugen Bircher, who led the Schweizerischer Vaterländischer Verband. In Letters to Suzanne (French: Lettres à Suzanne, Lausanne, Switzerland, 1949), the Swiss journalist Léon Savary retrospectively denounced in this sense "the occult influence of Hitlerism on the Swiss people during the Second World War, which they were not conscious of being under". German violations Nazi Germany repeatedly violated Swiss airspace. During the Battle of France in 1940, German aircraft violated Swiss airspace at least 197 times. In several air incidents, the Swiss shot down 11 Luftwaffe aircraft between 10 May and 17 June 1940, while suffering the loss of three of their own aircraft. Germany protested diplomatically on 5 June and with a second note on 19 June which contained explicit threats. Hitler was especially furious when he saw that German equipment was used to shoot down German pilots. He said they would respond "in another manner". On 20 June, the Swiss air force was ordered to stop intercepting planes violating Swiss airspace. Swiss fighters began instead to force intruding aircraft to land at Swiss airfields. Anti-aircraft units still operated. Later, Hitler and Hermann Göring sent saboteurs to destroy Swiss airfields but they were captured by Swiss troops before they could cause any damage. Skirmishes between German and Swiss troops took place on the northern border of Switzerland throughout the war. Allied bombings and violations Allied aircraft intruded on Swiss airspace throughout World War II. In total, 6,304 Allied aircraft violated Swiss airspace during the war. Some damaged Allied bombers returning from raids over Italy and Germany would intentionally violate Swiss airspace, preferring internment