Totally new to this site, and not an historian. But... no other answer is considering weapons. AFAIK Switzerland doesn't/didn't make its own weapons. Once the war is started, anything spent or destroyed by the enemy won't be replaced. Switzerland is neutral, so it has no allies to provide them with weapons/ammunition, and even if they are/were rich enough to purchase abroad, there are procurement delays, and the enemy can intercept the delivery. So if the guerilla could last, the military would lose a war of attrition (however expensive it would be for the enemy, given the tactical difficulties).

No, Switzerland was not self sufficient food wise. While the mountainous terrain is an advantage militarily, it is a big problem when you can't trade with your neighbors.

occupying the country would be relatively easy for the same reasons, hunger humbles even the most determined.

I would bet a three month blockade, and air campaign (on critical infrastructure) and the swiss would surrender.

Welcome to History.stackexchange

Your question is interesting, and a lot of points were highlighted by other contributors. I would like to add some points:

We are in a World War, not only in the fight of Axis/Germany versus Switzerland. One of the contributor spoke in the conditions of an uchrony where the Axis is victorious. What could be interesting is to consider the different periods when Axis could have invaded Switzerland.

Hindisght: I am not considering here the causes: why would Axis invade Switzerland, but only how it could do it without leaving to the Allies all the other fronts.

1939: Germany is the only fighter of the Axis: it could not invade Switzerland at the same time as Poland, without creating a frank reaction from the French and English armies. So if any reason leads Germany to threaten Switzerland, Germany would wait 1940.

1940: The best year considering the strategy: While attacking Belgium, Germany could also creates a new front on the right flank of the Allies. It would be somehow a way to secure the southern flank of the Sedan Breakthrough. Italy could help, and after the Anchluss, the Axis have three directions from which to attack Switzerland: North, East and South. However, as others said, the mountains are a great obstacle: the French defended with a great efficiency the Alpes, so the Swiss Army could have done the same. At the end, it is probable that the bulk of the Wehrmacht would have concentrated against France, winning the war and reaching Geneva from the West before the center of Swiss is reached from the East/North/South. This would be the perfect conditions for the Swiss Army to become an important Resistance movement.

1941: The perfect year on a tactical point of view: attack from all sides, with the same fights as against Yougoslavia or in Greece, with panzerdivisions having a good dotation in infantry and artilery, and a massive support from the Luftwaffe. Siwtzerland stood no chance but could resist for a long time.

1942, 1943: those years are the same: not that much troops available, with all the fronts, but for example, the troops used against the Yougoslavian Resistance movements could be directed against Switzerland. The RAF would be too far to support Swiss aviation, however a lot of bombers and fighters would be distracted from the major fights on the East Front and in Africa.

1944: The advance in Italy would lead Switzerland to be an opportunity for the Allies: so maybe the Axis will not take the risk to have a front in the back of Kesselring's troops in Italy.

1945: No way! The Allies are at the gates, not any troops are available to defend Switzerland.

Probably not impossible, as any country can invade another, but if you mean conquer it'd be quite hard, as the Alps would hinder German movement, and there wasn't any real motivation to invade Switzerland, as Switzerland is a mainly German country that focused on neutrality and didn't have any good resources the German war machine needed like oil. The only way I can see an invasion happening is if Germany decided to go thru the Maginot line with Switzerland instead of Belgium, which would strategically be a bad idea as Belgium's terrain is much more flat than the Alps.

Here's the answer to a silghtly different, but highly relevant question:

Why didn't Germany attack Switzerland?

There's a multitude of reasons, in no particular order (all links in German):

• Luck (source 1)
• Military deterrent (source 1)
• Lack of a good logistic opportunity for the Axis (source 1)
• Willing partner in trade (source 1)
• North south transportation, through the Gotthard tunnel, and the expected collapse of said tunnel in case of invasion (source 2)
• Germany's long term strategy of generating support among "Aryan" countries and "Aryan" occupied territories (source 3)
• Expectation of eventual peaceful annexation (source 3)

Any one of these reasons, with the exception of the first one, is not a sufficient explanation on its own. Taking the Swiss Plateau, installing a German friendly government (or rather, keeping the half that was German friendly already), and hoping that the army in the mountains eventually surrenders would have been a simple and viable strategy that the Germans were well aware of.

The Reich annexed or invaded various other Germanic territories, such as Austria (before the war even began), as well as Denmark, Norway, Belgium, Netherland, and Luxembourg (after it started). More to the point, the Low Countries, as Switzerland, also adopted, initially, a position of neutrality, so your question is certainly reasonable. I believe one of the reasons behind this inaction to be Switzerland's geographical, historical, cultural, national, and strategic ties to one of Germany's most trusted allies during the Second World War, namely Fascist Italy. (Indeed, Hitler's own Beer Hall Putsch was modeled on Mussolini's March on Rome). Of course, Austria also bordered on Italy, but, unlike Switzerland, it was not home, historically, to any significant Italian population. All other lands, however, were either mostly Germanic, or housed French and Slavic populations, whose (main) fatherland Hitler planned on attacking anyway. It is indeed rather striking that Germany's incursion into Italian territory (in the Alps and Adriatic) begins only after Italy's signing of the September 1943 Armistice with the Allied Forces. (Just my two cents).

Not impossible, but costly and difficult, to the point of being a net-negative.

I've been to Switzerland and more in other parts of the Alps (Austria and Germany). I'm also interested in history and military strategy. Based on what I've read over the years:

Invading Switzerland is a hard problem due to geography. There is a limited number of roads open all year, and of course the Swiss known them very well. There are hidden bunkers and guns everywhere, just look at these hidden bunkers for examples. When literally everything can be an anti-tank gun waiting for you to come into range, you can either accept terrible casualties or make your invasion a crawl.

Holding any conquered territory suffers from similar problems. Most villages and towns are at the bottom of valleys (where rivers and arable land are, you know?) and a few snipers in the mountains can make your life hell while your chance to get them is effectively zero.

Unlike Greece or Yugoslavia, most of the country is that kind of territory.

As for starvation - mountains are more complicated than that. There are so many Alms (mountain pastures) in the Alps that you can easily feed a widely distributed guerilla force from those alone. When you look at a mountain from below, it might seem that it goes up, gets rocky, and then there's the top. But in reality, there are vast areas of land up there, hidden from down by the mountain face. I've been climbing and skiing in the Alps and there are so many places I've been to that were completely invisible from below. You can put entire villages up there and from the valley you would never guess they even exist.

So you would have to run continuous patrols in a difficult terrain that your enemy knows like the back of his hand. If you want to know how that typically turns out, remember the Vietnam war.

And all of that for a small country with almost no strategic value and few ressources.

Question: I'm simply asking if the defense of Switzerland during WW2 was overrated. Many people claim that the country was impossible to occupy, I just want to know if this is not clearly exaggerated.

It is a myth that Switzerland was impossible to invade or occupy. Hitler in 1940 described Switzerland as a "pimple on the face of Europe", as he developed his plans to invade. Operation Tannenbaum.

Why he never invaded is reflected in timing and reward more than an aversion to doing battle with the Swiss army or on Swiss terrain.

Yes, Switzerland improved its defenses at the ontset of WW2. Yes, the mountains and terrain of Switzerland would make the invasion harder. But does anyone believe Switzerland's Alps and army were a greater deterrent than Russia's vast distances and cold winter, both of which defeated Napoleon? Or France's well equipped and significantly larger army? Or Britain with her Navy, RAF and Channel? Or the United States with an entire Ocean and vast population? Germany was at war with all these more existential threats rather than the Swiss.

Hitler's aversion to invading Switzerland came down to timing and reward. He was waiting for the time, and he really already had most of the reward a conquest of the Swiss would grant him.

Timing
Hitler was busy with the allies. If and when Hitler was free of them, popular wisdom is he would have invaded Switzerland. He already had his plans drawn up. The only thing which saved the Swizz was he likely hadn't gotten around to them yet.

Reward
Basically there was precious little reward for Germany in invading Switzerland in WWII. Germany was Switzerland's main trading partner before and during the war. On Switzerland's side, Switzerland is and was an industrial country with very few raw materials to fuel its industry. During WWII much of that fuel in the form of coal and raw materials came from Germany which surrounded Switzerland.

The Economics of Neutrality: Spain, Sweden and Switzerland in the Second World War (2011) - page 294
Between 1939 and 1945 Germany exported 10,267,000 tons of coal to Switzerland. In 1943 these imports supplied 41% of Swiss energy requirements. In the same period Switzerland sold electric power to Germany equivalent to 6,077,000 tons of coal.

.
Germany enjoyed the benefits of Switzerland's industrial output for important war materials such as ball-bearings. Germany also enjoyed the ability to transport goods through Switzerland on her railways to Germany's primary ally in Italy. Germany also enjoyed a brisk business with Switzerland's banks where they squirrelled away their loot and booty from across Europe. So overall there was very little to entice Germany to invade, they already realized the benefits of good trade, travel and cooperative relationship with Switzerland. Truth be told, these things didn't stop Hitler from invading Austria. Which brings us back to timing.

NY Times: The (Not So) Neutrals of World War 2
''The romantic idea of the Swiss citizen army standing between it and disaster in the war was always nonsense,'' said Arno J. Mayer, a professor of history at Princeton University. ''Given the fact it borders Germany, it was natural for it to lean more toward the Axis powers. It is the new spirit of our times that has led to the current scrutiny.''

There was a documentary last year if I remember well on French/German tv Arte which covered the subject, and its point of view was that despite what Swiss people like to think, they were not the hedgehog in German feet, but more likely the bankers of the third reich, so it had nothing to do with military.

It was explained that in this time, no country in the world wanted to be paid in mark for trade, and Germany desperately needed some raw materials for its war effort. There were two examples I can remember of materials they needed: rubber for tank caterpillar, and tungsten for tank armouring, coming essentially from a mine in Portugal for the last one.

And in all these situations, or when trade couldn't happen directly between Germany and Portugal for example, it was Switzerland who played the role of intermediate: Germans payed Swiss with the gold they stole from occupied countries (including jews), and Swiss payed Portugueses either in Franc or with gold. So they could not afford to loose their only way to trade abroad and left them alone.

In this French article covering the Portuguese issue, it is mentioned an amount of 40 tons of gold coming directly from Germany and another 120 tons having transited from Switzerland.

In this other French article, it is written than 80 percent of German gold used abroad by the Reichsbank during world war II transited through Switzerland.

The documentary demonstrated that despite the Allies unofficial warning made to Switzerland in 1944, trade still occurred however, at a lower rate. If I remember well, they talked about a last deal which was paid by gold molten from teeth taken in the camps...

A deal was signed in Washington in May 1946, unfreezing Swiss assets blocked by USA and withdrawing from blacklist name of Swiss companies who traded with Axis during the war, in exchange of 250M CHF.

The last part of the doc was explaining how hard it was in Switzerland nowadays to face this part of their History, especially because they built and where grown with a more glorious legend of the small hedgehog resisting victoriously to the German ogre.

I'll try to find the name of the doc tonight, it was a good watch.

Edit: I think it was this one, in French

Impossibility of an invasion

My answer is based on wikipedia article Operation Tannenbaum, which is about German plans for war against Switzerland during WW2:

Germany started planning the invasion of Switzerland on 25 June 1940, the day that France surrendered. At this point, the German army in France consisted of three groups with two million soldiers in 102 divisions.

[..]

The German plan continued to undergo revision until October, when the 12th Army submitted its fourth draft, now called Operation Tannenbaum. The original plan had called for 21 German divisions, but that figure was downsized to 11 by the 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 forest-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 Axis plans were to invade Switzerland with somewhere between 300,000 and 500,000 men.

This means that Germany considered a force of 11 of its own and 15 Italian divisions enough to invade and conquer Switzerland. This number represents only a small part of its forces at the time. There is no doubt that an invasion would have been possible and ultimately succeeded.

If Germany didn't invade Switzerland, it wasn't because of an unsurmountable Swiss military strength but because of a cost-benefit analysis.

Costs and benefits of an invasion

In the case of an invasion the lowlands in northern Switzerland would have been taken quickly. However, the bulk of the Swiss forces would have continued to resist for months in the mountains (National Reduit) and even after defeating all regular forces guerilla attacks would have continued. The war-torn (and at that time much poorer) country wouldn't have provided many resources but instead required a substantial and permanent military presence. Furthermore, a long-lasting and bloody war against Switzerland - and in particular its German(-speaking) population - would have been highly unpopular in Germany and among the soldiers as there were no historical grievances to exploit.

On the other hand, Germany could benefit in some ways from a neutral, pliable Switzerland. The Swiss industry was heavily reliant on Germany for coal (Germany provided 41 per cent of Swiss energy needs according to Was Switzerland neutral or a Nazi ally in World War Two?). In exchange Germany acquired many products from Switzerland, including arms, and benefited from Swiss banking and railroad connections to Italy (which would have been destroyed in case of an invasion).

Shields up!!!

It was advantageous for the Germans not to conquer Switzerland, and this would be a major factor in deciding the merit of doing so. A few only examples:

Switzerland provided the Nazis access to bank accounts and "safe" deposits of Jews and others. Exactly how these were divied up is unknown to me, but one can safely assume that the Nazis did not get 100% of the take. Without Swiss cooperation you would be far more liable to get a situation such as with the French art treasures which were very largely spirited away by the French (with assistance by the German assigned to "protect them for the Germans).

The Swiss were the international 'good-guys' [tm] who controlled the distribution of Red Cross parcels. They colluded with the Japanese to divert a substantial proportion of the funds intended for Red Cross Food Parcels intended for Allied prisoners of War in Japanese hands, and divided the spoils between them. While that is Japan and not Germany, I'd be surprised if the idea came to them that late in the piece.

I believe these answers are based on factual accounts of Swiss actions.
By all means disabuse me of this impression if appropriate.

This is an hypothetical question. I'll try to answer based only on the military concept.

You have already answered your own question, in part 4. You don't need to conquer the whole country; only the main cities and the fields are desirable. Forget about the mountains; you don't need them. Once in a while they'll have to attack some places to prevent guerrilla activities, but no more than that.

That is what happened in Yugoslavia and in the early stages of the invasion of Russia. The attack was so fast that the country did not have time to defend, so some people with military preparation defended themselves as guerrillas. Woods, swamps, deserts, jungles, and mountains were not occupied, so guerrillas went there.

Remember that from military point of view, you only need to destroy the enemy capability to resist and fulfill your political objectives. You don't need to occupy the whole territory; there is no need for that.

Think of the war in North Africa. The war only happened near the coast and in some oasis, not in the whole Sahara, and there isn't any need to fight there.

Think in the war in the Pacific. Several islands where ignored, while only the important ones were invaded.

Finally, think in the territories occupied by Germany and Japan at the end of the war. The allies did not need to occupy them before the end of the war. They only arrived there after winning the war.

There were many practical reasons why Switzerland was not occupied

• of which none of the first answer of @AmorphouBob apply

Some of these reasons are:

• militarily Switzerland was considered a 'thorny' problem, as expressed in the question and the Swiss strategy
• there was no strategic advantage (Switzerland was surrounded by the Axis powers)
• an economic disadvantage as a source of foreign currency and products
• an disadvantage of the loss of information from Allied areas (weekly air fights from Britain, with newspapers etc.) (source not yet found)

Further details about Switzerland in World War II, dealing with the first 3 points in more detail.

Please forget everything you learned about Germany during WW2 from TV series like Hogan's Heroes, where the people are portrayed as bumbling idiots.

They were everything but.

They knew exactly what they were doing and almost succeeded

• taking over a greater part of Europe
• mass murder of millions of deemed 'undesirables'
• destruction of whole countries
• corruption of generations of people
• and a list that is almost endless

There is no need, at every opportunity, for others to invent, at every opportunity available, something new based on that persons imagination and (it would seem) their need to add, over 70 years after the horror ended, a new scene to a Hollywood film or television series.

• the verified, factual facts are more than sufficient to portrait what horrors humans are capable of

Answer:

Switzerland was not occupied because it was not in the interest of Germany to do so, during that period of time, for the above given reasons.

The Germans were certain they could. For instance, their 1940 plans for Operation Tannenbaum estimated that a force of 300,000 to 500,000 men would have been sufficient.

Swiss military leadership also thought that an invasion would have been successful: Their revised military plan for the event of an invasion, the Réduit national, called for a delaying action at the border to allow the majority of the army to withdraw into mountain fortresses, effectively ceding control of all major population and industrial centers to the enemy.

In summary, neither side doubted that a German invasion would be successful if a sufficient proportion of Germany's military might were allocated to that task. It's just that Hitler had different priorities at the time. In Hitler's own words:

Die Schweiz, das kleine Stachelschwein, nehmen wir im Rückzug ein

In English:

Switzerland, the small porcupine, we'll conquer on the way back.

(Granted, the quote is from an earlier time in the war, but it is such an apt summary of Germany's leadership's dismissive attitude towards the Swiss military, that I thought it relevant anyway)

What factors were Hitler's / Germany's motivations for WW2? Revanchism, stealing raw materials, and racial hatreds.

The Swiss are largely German-speaking / Germanic, so there's no "racial superiority" factor to promote invasion and de facto depopulation/extermination and colonization.

They don't have a excessive amount of arable land for "true German" settlers.

Given their neutrality, they were no threat to Germany, and were probably convenient as a neutral middleman.

They weren't an easy target (either culturally or geographically) like Denmark or the Low Countries.

An invasion would have been fiercely opposed, and a distraction from Barbarossa.

No country is impossible to invade. Andorra could invade the USA.

The question you should have asked was "Was Switzerland Impossible to Conquer during World War II?".

The answer is no country is impossible to conquer. But there is great variation in the probability that a specific country will actually conquer another specific country if it tries to do so during a specific moment in time.

So the question you really should have asked was "How Hard Would it Have Been for the Axis to Invade and conquer Switzerland During World War II?"

A big part of Switzerland is highly mountainous. The Swiss army trained a lot of conscripts who went into the reserves after serving a short time and could be activated to serve in war. The Swisss government established various fortifications in the mountainous regions to hold out against hypothetical invaders.

Switzerland would have been harder to conquer per unit of territory or per unit of poplulation than many other European countries were. Starting an unnecessary war with Switzerland while World War Two was being fought would have been foolish.

Hitler is criticized for starting wars with the USSR and the USA while the war with Britain was ongoing, but Hitler wasn't totally reckless. He felt that the USSR would probably attack Germany in the future and thought he needed to attack the USSR first before they were ready, and he considered the USA to be already actively supporting Germany's enemies.

Switzerland wasn't threatening to attack Germany and it was surrounded by Axis powers so it couldn't export anything to help the Allies against the will of the Axis, and the Swiss government usually tried to be as neutral as possible, and to seem to other states to be neutral.

So basically even Hitler could see no reason to invade Switzerland during World War TWo when it would have a diversion of military resources from fighting more powerful and immediately threatening enemies.

Even though the Axis countries invaded a lot of countries during World War II, there were a number of other countries they didn't invade. Obviously the Axis leaders didn't consider the desirability of invading those countries worth the trouble at the moment.

Considering that the Axis invaded the mighty USSR and declared war on the mighty USA, I expect that if the Axis won World War II, had millions of soldiers available, and was sufficiently motivated to invade Switzerland, they would have invaded and conquered Switzerland despite the problems and difficulties.