Why was Stalin surprised by the German attack in June 1941?

There were some letters found frm hitler not so long ago found in which he writes stalin that he just sets up his troops at the border to the udssr bc the british RAF couldn'reacht them there. Also he was informed from several high ranking soviets reports that hitler will attack but also one which said the opposite in which Stalin and some high ranked soviet minister(or something) believed in. This behavioour can be seen as part of the great purdge and stalin fear to trust anybody around him.
I have to look up the sources and names at home. So if I find time the next days I will send them.

No one knew the exact date of the attack. Intelligence gave different data. Nevertheless, in the beginning of June, a latent mobilization began. Part of the divisions were sent to the border. Stalin was waiting for the invasion. He was preparing the country. Stalin believed in Hitler? No. Was ready for war? Yes. Was the Red Army ready? No no no. Absolutely not. Rearmament was to be completed in 1942. Stalin was surprised by the defeat of the Red Army? I think no. The "Winter war" showed the errors of military theories of Tukhachevsky. The Red Army was not ready for war. Wehrmacht was stronger.

Stalin failed to be objective. Leaders of totalitarian regimes often seem to suffer from this defect. Stalin was the center of a system where he didn't need to be objective and that revolved around his wishes. Absolute power tends to erode one objectivity. The prevalence of yes men and a reluctance to bring evidence that the supreme leader, conclusions counter to the leader's desires are just not presented forcefully. Stalin was used to a situation where he could almost control the facts, reality for most Russians was what Stalin said it was, fear of Stalin was greater than fear of getting things wrong. Stalin didn't want to face the facts that the had got things wrong, the system he was the center of was very much an enabler of Stalin's desires.

Because he was busy attacking Romania

https://en.m.wikipedia.org/wiki/Soviet_occupation_of_Bessarabia_and_Northern_Bukovina

Other priests were arrested and interrogated by the Soviet NKVD itself, then deported to the interior of the USSR, and killed. Research on this subject is still at an early stage. As of 2007, the Christian Orthodox church has granted the martyrdom to ca. 50 clergymen who died in the first year of Soviet rule (1940–1941).[86

Suvorov, The chief culprit (Naval Institute Press, 2008, pp. 248-9)

Golikov’s impunity for obviously wrong intelligence had been worrying me personally for a long time, until I attended a lecture in the Academy of the GRU. Later, when I was working in the central apparatus of the GRU, I found confirmation to this answer.

Golikov used to report to Stalin that Hitler was not preparing for war against the Soviet Union. It turned out that Golikov was reporting the truth to Stalin, since Hitler was not making such preparations. Golikov knew that Stalin did not trust documents. Golikov did not trust them either. He therefore looked for other indicators which would unerringly signal the moment when Hitler began his preparations for war with the Soviet Union.

[sheep farming, lubricating oil]

But Hitler launched Operation Barbarossa without making any preparations. Stalin, therefore, had no reason to punish Golikov. Golikov had done all that was humanly possible to discover German preparations for war. He told Stalin that no preparations were taking place, and this was the truth. There had only been a great buildup of German troops. Golikov gave instructions that not all German divisions had to be targets of attention, but only those that were ready to invade; those were divisions that had 15,000 sheepskin coats in their depots. There were simply no such divisions ready for war in the entire Wehrmacht.

I have read all the interesting answers and I want to propose a somewhat different way to look at this problem. By the way, this mistake of Stalin had cost millions of lives so the question is really important.

I believe, as did Molotov who experienced it firsthand, that Stalin was a genius of the first caliber. An evil genius, surely, but a political genius like no other. He controlled everything, he saw further and deeper than everybody and he was a practical and extremely ruthless leader and organizer. Even Churchill, who hated communism deeply, spoke of Stalin in such terms.

Stalin had the best intelligence service ever. Communists and communist sympathysers were everywhere and many of them were Comintern agents. He had informers in the German foreign office and General staff of the army. He was well informed on the German economy, the size of its army, its armour, the size of its air-force (Luftwaffe). He knew very well that the German tanks are greatly inferior to the Russian tanks. And he believed, crucially, that for Hitler to attack Russia would be suicidal. In this he was right of course, but still it was close. There were moments in 1941 and the summer of 42 when many in the west and perhaps also in Russia thought that the Wehrmacht is winning.

So why did he make his awful error? Hitler's chain of successes, culminating in the easy defeat of the British and French in 1940 left an impression in Stalin's cunning and calculating mind. "Perhaps the guy is not just a fanatical ideologue and adventurous gambler. He clearly has an excellent army so one can assume that his great gambles were based on a rational calculation". If so then Hitler would surely understand that attacking Russia is too dangerous and could even be suicidal!

So, Stalin's mistake was, in my opinion, that he gave Hitler too much credit. They were both representatives of the devil on earth but Stalin was by far the more able man.

Finally I would like very much to know what you think of my suggestions. I have been pondering this for a long time and am eager to discuss the matter.

Stalin received a large number of contradictory puzzle pieces. He and his intelligence analysts believed the information which suggested no attack yet and disbelieved the information which suggested an immediate attack.

• Stalin and his immediate circle must be blamed for creating a dysfunctional intelligence system, where analysts could not contradict the preconceived notions of the boss. Compare the recent Gulf War intelligence failure.
• Germany had a rather chaotic system of making policy, which explains why it was difficult to discern. That explanation falls flat in the last days before the attack.

I don't know a ton about this topic, but in Molotov Remembers, a reprint of a bunch of conversations with Molotov in the 70s and 80s, the interviewer asks a lot of questions about this topic.

Molotov said that Stalin knew there would be war with Hitler, and the whole point of the Molotov-Ribbentrop Pact was to stall for time and prepare, and that Stalin felt the country needed two more years before the USSR was ready. Molotov makes clear that all of the ruling circle knew that the Nazis were enemies, and that they knew an attack was eminent. Molotov laughed at the idea that Stalin naively thought that Hitler could be trusted to keep the terms of the Pact - indeed he points out that Stalin trusted no one, even Molotov himself!

So why was the Soviet Union "caught by surprise" when the Germans attacked? Molotov says that Stalin was primarily worried about an anti-USSR German/British alliance, and that Stalin sent orders to his troops specifically to make sure that Germany was the clear aggressor. The orders specified that there was to be no military response to anything the Germans did, except from Stalin himself.

Prior to the invasion, there was a number of border skirmishes and false alarms. Molotov says they were worried about being baited by Hitler into escalating the war, and thus be blamed for its start. The orders helped delay the start of the war by weeks or months. He also mentioned the British intelligence report and that they felt it was something of a joke, that "how could we not know the invasion was eminent? And how could we trust the British?"

Molotov then goes on to call Stalin a genius for this tactic, because:

1. The delayed the start of the war allowed winter to interrupt the German invasion, ultimately preventing defeat.
2. That showing that Germany was the aggressor split the German/British/capitalist alliance, and even causing the counter-intuitive US/British/Soviet alliance. Molotov states that receiving material help from the US was unthinkable in the 1930s, and that only Stalin could have conceived of this plan.

Just to be clear, I have not read enough about this subject to give a full answer, having only read Molotov's biased opinion. I am not sure I fully buy his opinion, considering what he said about the Holodomor. However, I feel he is correct in stating that the USSR would have lost if the invasion had started even 1 month earlier. I also liked his point about how odd the idea of an alliance with the British was.

On another note, it was interesting to hear his first hand account of what all the major actors in WWII were like personally; he didn't like Ribbentrop very much!

David Glantz in his book Barbarossa: Hitler's Invasion of Russia 1941 mentions several contributing factors.

• Stalin wanted to believe that Hitler would hold to the Molotov-Ribbentrop pact. This is the main one that usually gets brought out, but it's not the whole story.
• When German forces started building up on the Soviet border, Germany told the Soviets that this was for staging exercises for the invasion of Britain well away from potential British observation. The German invasions of Yugoslavia and Greece also gave a plausible reason for German forces to be in the east.
• Stalin believe Hitler was too rational to launch a war against the Soviet Union whilst not having finished off the British in the west. Hitler turned out to be not as rational as that.
• Stalin was expecting and preparing for a war with Germany possibly in 1942, and there is a human tendency to confirmation bias: to look for evidence that supports our preconceptions and put less weight on stuff that contradicts it.
• Stalin's purges had not only affected the armed forces, but also the intelligence services which were therefore institutionally less experienced and prepared. And their reports to Stalin had a tendency to be massaged to fit his preconceptions: evidence of German possible aggression were downplayed; examples of German forces showing restraint were emphasised. Telling Stalin things he didn't like wasn't a life-enhancing move, and that had the effect of distorting the intelligence to reinforce his hopes of no immediate attack.
• In May 1941 Berlin and the OKW encouraged rumours that Berlin was planning to demand changes to the agreement between the Soviet Union and Germany. This encouraged the belief that there would be some kind of ultimatum before any attack to serve as a pretext.
• Early, accurate warnings of German intentions had 15th May as the start date, which was indeed the German plan originally. The invasion of Yugoslavia and Greece ended up delaying Barbarossa, which had the effect of discrediting the agents who had actually provided accurate information. Several more specific dates were reported and also passed without incident, so there is a "boy who cried wolf" scenario here where repeated warnings of German attack on specific dates all prove false, again undermining the reports of imminent attack.

It is very easy after the event to pick out the bits of intelligence that should have warned the Soviet Union. It is much harder before time to identify which of the many contradictory bits of intelligence you should believe and which are misinformation or just inaccurate (or were accurate before plans changed). Looking at the information available to Stalin at the time, it is perhaps less surprising that he was taken by complete surprise in June 1941, although certainly his wishful thinking was one of the contributing factors as well.