for example people don't fully appreciate how much USSR helped Nazi Germany in starting WW2 - there was cooperation in tech, industry (last train with Soviet resources left to Germany literally a few hours before Barbarossa) and in military - German tankers even used to conduct exercises on Russian steppes (of course in Spain they ended up supporting different sides - but that's not that uncommon in politics).
But in 1933-41 there was pretty much a silent alliance between these two - without Soviet resources Germany would not've been able to build it's war machine. After 1941 these resources were among the top 3 reasons why we lost the war (oil shortages had a very debiliating effect on German war machine)
There was a very close relationship between Germany and the Soviet Union... for a start they both got screwed and lost territory after WWI rather unfairly in both cases I might add... the Germans and Russians were no more to blame for WWI than any other country including France, the US or UK.
All cooperation ended in 1933 however and military cooperation ended then too.
After 1933 the only relationship was commercial... the Soviets sold material to Germany... that was it.
If Germany and the Soviets were actually allies there would be no need for a non aggression pact like the molotov rippentropp pact.
Of course the Soviets and the Germans would appreciate the use of tanks in future war... for the most part the war in the east in WWI was not static trenches like it was in the west... for the west the tank was seen as a solution to the problems of machine guns and artillery in trench warfare... in the east... ie Germany and the Soviet Union it was more about mobility and fire power.
BTW if you want to point the finger for prewar collaboration then how about US companies like what became IBM selling the Nazis the counting machines they used to collate records to find jews in occupied territories, so they could efficiently round them up when the time was right.
Chamberlain was happy to appease Hitler along with the rest of the west.
German High Command never thought seriously about invading Britain. In order to succeed in that Germany needed AT LEAST a British-sized navy or preferable, absolute rule over the seas... Normandy landings come to mind immediately. With USSR at least there was a chance of knocking it out for some years - but ultimately it was not possible either. It all boils down to numbers.
Rubbish... over such a small area, a strong air force could ensure local superiority for the time needed to mount an attack... their problem wasn't lack of aircraft carriers and battleships, it was a lack of appropriate landing vessels. In the 1920s the Soviet Airborne forces could land groups of men in 20,000s with equipment... with a modern transport fleet the Germans would have been able to do the same with the right investment.
Lets face it... if the Germans had just concentrated on airfields and radar stations the battle of britain would have been lost... without air cover, they could have gone over Dunkirk style...