http://en.wikipedia.org/wiki/Operation_Tannenbaum
Germany started planning the invasion of Switzerland on 25 June 1940, the day France surrendered. At this point the German Army in France consisted of three army groups with 2 million soldiers in 102 divisions.[10] Switzerland and Liechtenstein were completely surrounded by Occupied France and the Axis Powers, and so (Swiss General Henri) Guisan issued Operationsbefehl Nr. 10, a complete overhaul of existing Swiss defensive plans. The St. Maurice and St. Gotthard Passes in the south and the Fortress Sargans in the northeast would serve as the defense line. The Alps would be their fortress. 2nd, 3rd, and 4th Army Corps were to fight delaying actions at the border, while all who could retreated to the Alpine refuge known as the Réduit national. The population centers were all located in the flat plains of the north, however. They would have to be left to the Germans in order for the rest to survive.[11]
Hitler demanded to see plans for the invasion of Switzerland. Franz Halder, the head of OKH, recalled: "I was constantly hearing of outbursts of Hitler’s fury against Switzerland, which, given his mentality, might have led at any minute to military activities for the army."[12] Captain Otto Wilhelm von Menges in OKH submitted a draft plan for the invasion. Generaloberst Wilhelm Ritter von Leeb’s Heeresgruppe ‘C’ (HGr. C), led by Generalleutnant Wilhelm List and 12th Army would conduct the attack. Leeb himself personally reconnoitered the terrain, studying the most promising invasion routes and paths of least resistance.[13] Menges noted in his plan that Swiss resistance was unlikely and that a nonviolent Anschluss was the most likely result. With "the current political situation in Switzerland," he wrote, "it might accede to ultimatum demands in a peaceful manner, so that after a warlike border crossing a rapid transition to a peaceful invasion must be assured."[14]
The plan continued to undergo revision until October, when 12th Army submitted its fourth draft, now called "Operation Tannenbaum." The original plan called for 21 German divisions, but that figure was revised downwards to 11 by OKH. Halder himself had studied the border areas, and concluded that the "Jura frontier offers no favorable base for an attack. Switzerland rises, in successive waves of wood-covered terrain across the axis of an attack. The crossing points on the river Doubs and the border are few; the Swiss frontier position is strong." He decided on an infantry feint in the Jura in order to draw out the Swiss Army and then cut it off in the rear, as had been done in France. With the 11 German divisions and roughly 15 more Italian divisions prepared to enter from the south, the Swiss were looking at an invasion by somewhere between 300,000 and 500,000 men.[15]
Hitler never gave the go-ahead, for reasons that are still uncertain today. Although the Wehrmacht feigned moves toward Switzerland in its offensives, it never attempted to invade. After D-Day, the operation was put on hold and Switzerland remained neutral for the duration of the war.
10. Ernest May, Strange Victory: Hitler’s Conquest of France (New York: Hill and Wang, 2000) 477.
11. "Operationsbefehl Nr. 10," June 20, 1940, Tagesbefehle des Generals.
12. Steinberg, Why Switzerland? 68.
13. Gerhard Weinberg, A World at Arms: A Global History of World War II, 2nd edition (New York: Cambridge University Press, 2005), 174.
14. Klaus Urner, "Let’s Swallow Switzerland": Hitler’s Plans against the Swiss Confederation (Lanham, MD: Lexington Books, 2001) 67.
15. Angelo Codevilla, Between the Alps and a Hard Place: Switzerland in World War II and Moral Blackmail Today (Washington, D.C.: Regnery, 2000) 57-58.
