Editing Case Blue (section)

===Opening phase===
[[File:Eastern Front 1942-05 to 1942-11.png|thumb|300px|The German advance from 7 May to 18 November 1942.
{{legend|#fff8d5|to 7 July}}
{{legend|#ffd2b9|to 22 July}}
{{legend|#ebd7ff|to 1 August}}
{{legend|#ccffcd|to 18 November}}]]
The German offensive commenced on 28&nbsp;June 1942, with Fourth Panzer Army starting its drive towards Voronezh. Due to a chaotic Soviet retreat, the Germans were able to advance rapidly, restoring ''Wehrmacht'' confidence for the upcoming major offensive.{{sfn|Beevor|1999|p=75}}

[[Close air support]] from the Luftwaffe also played an important role in this early success. It contained the [[Red Air Force]], through [[air superiority]] operations, and provided interdiction through attacks on airfields and Soviet defence lines. At times, the German air arm acted as a spearhead rather than a support force, ranging on ahead of the tanks and infantry to disrupt and destroy defensive positions. As many as 100 German aircraft were concentrated on a single Soviet division in the path of the spearhead during this phase. General Kazakov, the Bryansk Front's chief of staff, noted the strength and effectiveness of the Axis aviation.{{sfn|Hayward|2001|p=135}} Within 26 days, the Soviets lost 783 aircraft from the [[2nd Air Army|2nd]], [[4th Air Army|4th]], [[5th Air Army|5th]] and [[8th Air Army|8th]] Air Armies, compared to a German total of 175.{{sfn|Bergström|2007|p=60 |ps=. list of Red Air Force [[order of battle]] indicates these units were mainly in combat during ''Blau'', pp. 49–50.}}

By 5&nbsp;July, forward elements of Fourth Panzer Army had reached the [[Don River (Russia)|Don River]] near Voronezh and became embroiled in the [[Battle of Voronezh (1942)|battle to capture the city]]. Stalin and the Soviet command still expected the main German thrust in the north against Moscow, and believed the Germans would turn north after Voronezh to threaten the capital.<ref name=A40/> As a result, the Soviets rushed reinforcements into the town to hold it at all costs and counterattacked the Germans' northern flank in an effort to cut off the German spearheads. 5th Tank Army, commanded by Major General [[Alexander Liziukov|A.I. Liziukov]], managed to achieve some minor successes when it began its attack on 6&nbsp;July, but was forced back to its starting positions by 15&nbsp;July, losing about half of its tanks in the process.{{sfn|Glantz|House|2009|pp=149–153}} Although the battle was a success, Hitler and [[Fedor von Bock]], commander of Army Group South, argued over the next steps in the operation. The heated debate, and continuing Soviet counterattacks, which tied down Fourth Panzer Army until 13&nbsp;July, caused Hitler to lose his temper and dismiss Bock on 17&nbsp;July. As part of the second phase of the operation, on 9&nbsp;July, Army Group South was split into Army Group A and Army Group B, with Wilhelm List appointed as commander of Army Group A and Army Group B commanded by Maximillian von Weichs.<ref name=A40/>

Only two weeks into the operation, on 11&nbsp;July, the Germans began to suffer logistical difficulties, which slowed the advance. The German Sixth Army was continually delayed by fuel shortages. Eight days later, on 20&nbsp;July, shortages of fuel were still undermining operations, leaving many units unable to execute their orders. The [[23rd Panzer Division]] and [[24th Panzer Division]] both became stranded during the opening phase. Once again, as it had done during the [[Norwegian Campaign]] in April 1940, and ''Barbarossa'' in 1941, the Luftwaffe's [[Junkers Ju 52]] transport fleet flew in supplies to keep the army going. The situation remained difficult with German troops forced to recover fuel from damaged or abandoned vehicles, and in some cases, leave behind tanks and vehicles with heavy fuel consumption to continue their advance. This undermined the strength of the units, which were forced to leave fighting vehicles behind. Nevertheless, the Luftwaffe flew in 200 tons of fuel per day to keep the army supplied.{{sfn|Hayward|2001|p=142}} Despite this impressive performance in keeping the army mobile, Löhr was replaced by the more impetuous and offensive-minded Richthofen.{{sfn|Hayward|2001|p=143}}