What is Britain had not entered WWII

[ReluctantSamurai]

what if Hitler had ordered the invasion of the USSR there and then...how far would the Axis have advanced

Without all of the experience gained during the Norwegian and Low Countries/French campaigns, probably not as far as one might think. Co-operation between close air support from the Luftwaffe and armored formations, which was so crucial for breakthroughs, would lack the refinement gained though battle testing. And who commands? Guderian would likely still be in command of only a Panzer Corps instead of a Panzer Group; Hermann Hoth would still be commanding a Motorized Corps instead of a Panzer Group; Kleist would lack the experience of the Polish, France, and Balkan campaigns; Hoepner, like the other Barbarossa Panzer Group commanders would likely still be leading a Corps also. It was the experience of these commanders, as well as that of the tank crews, that allowed the sweeping advances during the initial stages of Barbarossa.

What would German armored formations look like? The Low Countries and France showed the PzI and PzII to be wholly inadequate, and the PzIII's 37mm was incapable of defeating the French Char bis or the British Matilda frontally. Numerically, the PzI/II constituted the bulk of German armored formations in 1940 into early 1941, so production of the PzIII would have to be greatly accelerated. Without battlefield experiences from previous campaigns, would that have happened? The T26, which constituted the bulk of Soviet Mechanized Corps, was inferior to the PzIII, but outclassed the PzI & II.

And I will repeat my earlier statement about one side being able to change in revisionist scenarios, but not the other. What if Stalin heeds the warnings that Germany is going to attack? Particularly if Hitler signs some sort of agreement with France and Britain to secure his western flank should Germany attack the Soviet Union. With better front preparation, with formations deployed in depth instead of crammed too close to the border (which aided the huge initial encirclements seen historically), and a German army with far less experience, and with lower quality equipment, how far do they get?