Maybe so, it's possible, though of course the Germans made another pitch to win in 1942 that had a chance.
Case Blue. One of the interesting German offenses in WW 2.
Eh, yes and no. I think that Case Blue was a relative longshot with only a remote chance of actually winning the war for the Nazi's. They had a not altogether impossible chance of cutting off Soviet access to the Caucasian Oil but their chances of actually acquiring the oilfields, a transportation network to refineries, refineries, and a transportation network to where the oil was needed were remote at best. Even if they had cut off Soviet access to Caucasian oil, the Soviets still had other oil and the US could have increased shipments as well so the Soviet War Machine wouldn't have suddenly stopped in its tracks completely (this is not to say that it wouldn't have been a problem for the Soviets and their allies).
IMHO, the only significant chance the Nazi's had to get a different result out of the war would have been to knock the Soviets out as the Kaiser had done in his war a quarter-century earlier. That, combined with having already occupied France and having Italy as an ally rather than an enemy would have presented the US and UK with an incredibly difficult proposition of trying to assault "Fortress Europe".
I know you know but most Americans don't realize that as important as the D-Day landings were, at the time 80% of the German Army was fighting the Soviets on the Eastern Front. There is simply no way that the US and UK would have been ready to make such a landing against an undistracted Germany for at least another year or two. Thus, had the Germans managed to knock the Soviets out, the war would have either been ended in some sort of Nazi/UK/US compromise or decided after the development of Atomic Weapons in 1945.
Knocking the Soviets Out:
Stalin is widely reputed to have gone into a virtual coma in the early weeks after the Nazi invasion. The bad news for the Soviets came swiftly and just didn't stop for months. The German advance from the frontier to the gates of Leningrad and Moscow is just astounding. I once read that when FDR's personal envoy to Stalin was travelling from Britain to Archangel aboard a British warship in late 1941 he wrote in his diary that "the English are consistent, since I've been with them they have been saying that the Soviets will hold out for another two weeks." It really was that touch-and-go for a while.
Plenty of historians will tell you that there is "plenty of land behind Moscow" and that the Soviets could have lost Moscow and stayed in the war but I'm not so sure. Moscow wasn't just a city or even the biggest city in the Soviet Union, it was also the largest manufacturing center, the transport hub, and the center of command and control. Finally, there is a psychological impact to losing your capital. In theory the Soviets could have just retreated some more and kept fighting but as a practical matter I'm not sure that they would have.
The Germans got incredibly close to capturing Moscow. One of the history books I have at home has a picture of a wrecked German tank with the spires of the Kremlin visible in the background. That is CLOSE. Maybe if they had focused on a single goal rather than changing priorities at Hitler's whim or if they hadn't had to spend the spring bailing out Mussolini's invasion of Greece they might have gotten there. If that had been enough to knock the Soviets out of the war then who knows if Churchill's government in the UK would even have survived. Remember that the US was still officially neutral (although providing billions of dollars worth of military and other supplies and fighting an undeclared naval war in the Atlantic against the U-boats). A Germany that had possession of all of France and what they wanted of Russia would have been far too much for the UK to face alone.
It is impossible to say what the ultimate impact of Germany knocking the Soviets out of the war would have been. It might have been decisive in their favor or it might simply have led to millions of additional German Civilian casualties as their cities were vaporized by Anglo-American Atomic weapons. That said, I think the Germans had a decent chance of accomplishing the goal of knocking out the Soviets in 1941 but not so in 1942 and beyond.
