Editing Case Blue (section)

===Splitting of Army Group South===
[[File:Przeprawa wojsk niemieckich przez Don (2-747).jpg|thumb|right|German motorcycle infantry cross the Don River on a timber bridge, July 1942. Abandoned Soviet vehicles and supplies are seen in the background.]]

Believing that the main Soviet threat had been eliminated, desperately short of oil and needing to meet all the ambitious objectives of Case Blue, Hitler made a series of changes to the plan in ''Führer'' Directive No. 45 on July 23, 1942:
* reorganized Army Group South into two smaller Army Groups, A and B;
* directed [[Army Group A#Eastern Front, 1942|Army Group A]] to advance to the Caucasus and capture the oil fields ([[Operation Edelweiß]]);
* directed [[Army Group B#Eastern Front|Army Group B]] to attack towards the Volga and Stalingrad ([[Operation Fischreiher]]).<ref name=A40/>

There is no evidence Hitler was opposed by, or received complaints from [[Franz Halder]], Chief of the General Staff, or anyone else, about the directive until August 1942. The new directive created enormous logistical difficulties, with Hitler expecting both Army Groups to advance along different routes. Logistics lines were already at breaking point with ammunition and fuel shortages most apparent and it would be impossible to advance using the conservative supply rates he demanded. The divergence of the Army Groups would also open a dangerous gap between the Armies, which could be exploited by the Soviets. The [[Alpini|Italian Alpine Corps]], of the [[Italian Army in the Soviet Union]], did not arrive in the Caucasus Mountains with Army Group A, instead remaining with Sixth Army. Army Group A was expected to operate in mountain terrain with only three mountain divisions and two infantry divisions unsuited to the task.{{sfn|Hayward|2001|pp=147, 149}}

The splitting of Army Group South enabled the launching of Operation Edelweiss and Operation Fischreiher, the two main thrusts of the Army Groups. Both groups had to achieve their objectives simultaneously, instead of consecutively.<ref name=A40/> The success of the initial advance was such that Hitler ordered the Fourth Panzer Army south to assist the First Panzer Army to cross the lower Don river.<ref name=G119>{{harvnb|Glantz|1995|p=119}}.</ref> This assistance was not needed and Kleist later complained that Fourth Panzer Army clogged the roads and that if they had carried on toward Stalingrad, they could have taken it in July. When it turned north again two weeks later, the Soviets had gathered enough forces together at Stalingrad to check its advance.{{sfn|Liddell Hart|1948|pp=204–205}}