Operation Tannenbaum (Operation Pine Tree) was the planned invasion of Switzerland by Nazi Germany during World War II.
Germany started planning the invasion of Switzerland on 25 June 1940, the day France surrendered. The third of these plans was called Operation Tannenbaum. The plan was submitted by 12th Army on 6 September 1940 to Army Group C.
Operation Tannenbaum was the third of several detailed invasion plans drawn up for the German General Staff after France collapsed, but Hitler never gave the go-ahead, for reasons that are still uncertain today.
There are several possible reasons that the Germans did not execute the plan:
Switzerland was not seen as a threat to Germany. Hitler had his thoughts first with the Battle of Britain (Operation Sealion: where the few available German mountain divisions were allocated) and afterwards with the invasion of the Soviet Union Operation Barbarossa (already in August/September 1940 large numbers of troops were moved to the East to counter the Soviet threat to Bessarabia).
The main window of opportunity for military action against Switzerland was the period between the Fall of France and October/November 1940. After this time, weather would not have permitted a real blitzkrieg attack due to the Swiss terrain. And after the winter 1940/41 Hitler was occupied by Operation Marita and Barbarossa.
Italian dependence on coal imports from Germany after the Italian declaration of war meant the use of an intact Swiss rail network was necessary to meet demand
While the Swiss military was markedly outnumbered by German forces in artillery and aircraft, to control the nation the Germans would have had to destroy a large and well-trained infantry force drawn directly from the Swiss population. The small arms of the Swiss, including the Schmidt-Rubin repeating rifle, were equal or superior to the best German small arms of the early war period, and Swiss marksmanship was well established. The example of the Winter War showed how a similar force of trained riflemen could stop a much larger, better equipped army. While revisionists have questioned the notion that Swiss rifles stopped the invasion, there can be no doubt that an invasion would have cost the Germans troops and resources needed elsewhere because of those rifles. Had there been no meaningful Swiss military force, the potential invasion would have been considerably less costly.
The Swiss government also had a decentralised structure, so even the Federal President was a relatively powerless official with no authority to surrender the country. Indeed, Swiss citizens had been instructed to regard any surrender broadcast as enemy lies and resist to the end.
Although the Wehrmacht feigned moves toward Switzerland in its offensives, it never attempted to invade. After D-Day, Operation Tannenbaum was put on hold and Switzerland remained neutral for the duration of the war. Actually the Germans were probably in no position to allocate the number of divisions required by Tannenbaum after the beginning of the invasion of the Soviet Union.
Some industrialists in Switzerland contributed to the German war effort by selling goods such as ball bearings and parts to torpedo guidance systems, manufactured in facilities that could not be bombed by the Allies due to the country's neutral status. The contribution of Switzerland to the overall Nazi German war effort is believed to have been less than 0.5%.
Some rumours suggest that Hitler had a personal sentiment toward Swiss culture and its art collections. The rumour generally suggests that Hitler feared that the panzers (and other armoured vehicles) would damage the rich history of Swiss cities, though that statement is debated.