The 'Donbas Defensive Operation' was the Soviet undertaking by the South Front and the left wing of the South-West Front within the 'Voronezh-Voroshilovgrad Strategic Defensive Operation' designed to halt the German 'Clausewitz' (i) strategic offensive (7/24 July 1942).

In Soviet history, the operation was sometimes divided into a pair of sub-operations known as the 'Valuisko-Rossosh Defensive Operation' and the 'Voroshilovgrad-Shakhty Defensive Operation'.

In the 'Blau' operations of its strategic campaign of the summer of 1942, the German high command had as its primary objective of defeating the entire southern flank of the Eastern Front, reaching the Volga river and capturing the Caucasus. Starting on 28 June, the implementation of the 'Blau' plan, the Germans achieved a rapid and decisive success in the Voronezh sector and deeply flanked the forces of General Leytenant Rodion Ya. Malinovsky’s South Front and the left wing of Marshal Sovetskogo Soyuza Semyon K. Timoshenko’s South-West Front from the north in a breakthrough to a depth of 106 miles (170 km) in 10 days. Taking advantage of this success, Generalfeldmarschall Fedor von Bock’s Heeresgruppe 'Süd' embarked on 'Clausewitz' (i), which provided for a deep-penetrating thrust by the forces of Generaloberst Hermann Hoth’s 4^th Panzerarmee, as the 4^th Panzergruppe had been redesignated on 1 January, to the south-east from the Ostrogozhsk region along the western bank of the Don river in the general direction to Kantemirovka and Rostov-na-Donu in order to make a complete encirclement of the forces of these Soviet fronts. At the same time, Generaloberst Ewald von Kleist’s 1^st Panzerarmee, upgraded from Gruppe status on 25 October 1941, was to cut through the South Front’s defences with a blow from the Artemovsk region to Voroshilovgrad and Kamensk-Shakhtinsky.

The tank armies were to be supported by infantry armies in the destruction of the Soviet forces which had been encircled, and then to develop the offensive: General Friedrich Paulus’s 6^th Army to Stalingrad on the Volga river, and Generaloberst Richard Ruoff’s German 17^th Army and General de corp de armatâ Petre Dumitrescu’s Romanian 3^rd Army to the Caucasus.

On 9 July, the third day of the operation, Heeresgruppe 'Süd' was divided into two army groups assigned to different aspects of the German operation. von Bock’s (from 16 July Generaloberst Maximilian Reichsfreiherr von Weichs’s) Heeresgruppe 'B' used its right-wing forces in 'Clausewitz' (i): these were Hoth’s 4^th Panzerarmee with the XL Panzerkorps, XLVIII Panzerkorps and XXIV Panzerkorps with 733 tanks, and Paulus’s 6^th Army with the XVII Corps and LI Corps with about 400 tanks. Generalfeldmarschall Wilhelm List’s Heeresgruppe 'A' deployed its full strength, which comprised von Kleist’s 1^st Panzerarmee with the III Panzerkorps and XIV Panzerkorps operating 654 tanks, Ruoff’s 17^th Army with the XLIV Corps, XI Corps, LII Corps, LXIX Gebirgskorps and LVII Panzerkorps, Dumitrescu’s Romanian 3^rd Army and Generale d’Armata Italo Gariboldi’s Italian 8a Armata.

The Soviet opposition to these Axis forces was provided by two fronts. The left-flank forces of Timoshenko’s South-West Front, which was in fact disestablished on 12 July, comprised General Major Aleksei I. Danilov’s 21^st Army, General Major Dmitri N. Nikishov’s 57^th Army, General Major Vasili D. Kryuchenkin’s 28^th Army, General Major Kirill S. Moskalenko’s 38^th Army, General Leytenant Anton I. Lopatin’s (from 14 July General Major Feofan A. Parkhomenko’s) 9^th Army and General Major Timofei T. Khryukin’s 8^th Air Army. At the start of the operation, Malinovsky’s South Front totalled 522,500 men and 214 tanks in General Major Piotr M. Kozlov’s 37^th Army, General Major Aleksei A. Grechko’s 12^th Army, General Leytenant Fedor M. Kamkov’s 18^th Army, General Major Viktor V. Tsyganov’s 56^th Army, General Leytenant Ilya K. Smirnov’s (from 15 July General Major Vladimir N. Martsinkevich’s) 24^th Army and General Major Konstantin A. Vershinin’s 4^th Air Army. After the operation’s start, the South Front was strengthened by the arrival of General Major Nikolai I. Trufanov’s 51^st Army. After the disestablishment of the South-West Front, Timoshenko’s Stalingrad Front assumed command of the 21^st Army, 62^nd Army, 63^rd Army and 64^th Army, and on 17 July this from also received from the South Front the latter’s 28^th Army, 57^th Army and 38^th Army. As a result of the loss of control and the intermingling of the front, however, this change was only partially fulfilled: the headquarters and a number of individual units of these armies reached the Stalingrad Front, but the rest of the troops remained in the South Front, and the armies themselves had to be re-formed.

After the German breakthrough toward Voronezh, the Soviet high command rightly assessed the overall strategic objectives of the German plan and on 6 July ordered the withdrawal of the South Front to the line linking Denezhnikovo, Trehizbenka and Krasny Luch. On the night of 7 July, the front began a well-ordered withdrawal. On 8 July, German troops began to press the South Front with the forces of the 6^th Army and the 1^st Panzerarmee. There was fierce fighting, but the Germans failed to break through the South Front’s defences. Farther to the north, however, on the South-West Front’s southern flank, the armour-led German attack was successful. Having attacked the heavily weakened troops of the 28^th Army and 21^st Army, which could offer no significant defence after their defeats late in June and early in July, by the end of 11 July, the 6^th Army and 4^th Panzerarmee broke through into the rear of the front to a depth of 112 miles (180 km), reaching the area of Dyogtevo, and created a threat to the South Front’s rear. At this point, the South-West Front’s headquarters Front lost effective control of its forces, and in the following days the 4^th Panzerarmee reached Morozovsk on 15 July and Millerovo on 16 July. Taking advantage of the difficult situation, the 1^st Panzerarmee, which attacked from the west, finally managed to break through the defences of the 37^th Army and on 18 July entered Kamensk-Shakhtinsky.

A major threat thus loomed over the South Front, despite the fact that its troops had withdrawn in a fairly organised manner and stubbornly defended themselves on the line to which they had retreated. The farther advance of the Germans to the south created a very real possibility of the encirclement of the Soviet forces in the Donbas, and of a German breakthrough to Stalingrad and the northern Caucasus. On 10 July. Iosif Stalin ordered Marshal Sovetskogo Soyuza Semyon M. Budyonny’s North Caucasus Front as a matter of urgency to take up defensive positions on the eastern bank of the Don river and block the path to the Caucasus region. On the same day Stalin ordered the acceleration of the construction of fortifications in the Stalingrad area for their speedy occupation by the formations of the 62^nd Army and the start of work on the construction of defensive lines in the rear of the South Front and South-West Front. Since the main direction of the German strikes on diverging axes was now clear, the South-West Front was transformed into the Stalingrad Front, which was reinforced with three reserve formations (37^th Army, 57^th Army and 9^th Army), and received the task of defending the approaches to Stalingrad. On 12 July, the 28^th Army was transferred from the South-West Front to the South Front.

Initially, the South Front was ordered to create a stable defence in the area of Millerovo, but in view of the Germans' deep penetration, by 15 July the front had received revised orders to withdraw its troops behind the Don river and create a defence along its southern reaches between Verkhne and Kurmoyarskaya, and farther along the line of the Rostov-na-Donu fortified area.

Meanwhile, fierce battles continued at the front, and the Germans clove through the defences of the 28^th Army and 57^th Army. These Soviet armies fought with great stubbornness and managed to avoid encirclement, but while part of them withdrew to the east the other part pulled back to the south. In the Millerovo area, parts of the 38^th Army and 9^th Army were surrounded: their main body was unable to break through to the south to rejoin the main forces of the South Front and was forced to break out of the encirclement to the east.

Thus, by 18/20 July, the northern flank of the South Front had been defeated. An attempt to restore the situation with a counterattack toward Millerovo by the 24^th Army’s reserve from the south failed: approaching Millerovo, the main force came under attack from the 1^st Panzerarmee and suffered heavy losses and as a result the Germans were able to effect a complete breakthrough. The Germans were thus in the position to undertake a major exploitation. On the orders of Adolf Hitler, the 4^th Panzerarmee realigned the axis of its advance from Stalingrad to Rostov-na-Donu, to which it moved at great speed. On 21 July the 4^th Panzerarmee entered Shakhty, on 22 July Novocherkassk and on 23 Rostov-na-Donu. On 24 July the Germans completed their seizure of Rostov-na-Donu although, the Soviets claimed, individual units continued to fight until 27 July.

The 56^th Army was unable to provide any determined and effective resistance in the Rostov-na-Donu fortified area and also to ensure the withdrawal of the South Front’s forces across the Don river. Although the Soviet troops were able to make use of the fact that there the encircling Germans were not able to create any continuous front, and the South Front’s main forces finally managed to fight their way to the southern bank of the Don river and create defensive positions there, the process was very costly in terms of men and equipment. The Germans managed to cross the Don river from the march, moreover, and seize a number of bridgeheads on the river’s southern bank.

The unsuccessful outcome of the 'Donbas Defensive Operation' was the result of a number of strategic and operational miscalculations by the Soviet high command. Firstly, the Stavka failed to make a valid assessment of the consequences of the Soviet defeat near Kharkov, and therefore did not promptly dispatch sufficient forces to create a stable defence in this area. Secondly, the high command reserves were transferred to the south only after heavy defensive battles had started, and then the reserves arrived on a piecemeal basis and could not turn the tide against the Germans forces. Thirdly, the South-West Front and South Front failed to organise a systematic withdrawal of the forces. Fourthly, the Rostov-na-Donu fortified region was not ready to offer a solid defence. Fifthly, the withdrawal of Soviet forces led all too often to the loss of communication between the fronts' and armies' commanders with their troops for several days, which led to a loss of control. And fifthly, the German command made the most of the great mobility of its troops, skilfully transferring significant forces to new directions and minimising the time they needed before launching new attacks.

During the 'Donbas Defensive Operation', the German troops failed to defeat and then destroy the southern and left flanks of the South-West Front and South Front, but nonetheless inflicted a heavy defeat on the Soviets, a fact which came to play an extremely important role in the future in several respects. Firstly, the Germans seized the strategic initiative on the entire southern wing of the Eastern Front; secondly, they created a direct threat to the Stalingrad region (the German 'Fischreiher' offensive against Stalingrad was launched during the operation on 12 July) and the northern Caucasus (the 'Edelweiss' offensive was launched on 25 July); thirdly, the South Front and South-West Front suffered heavy losses, which greatly weakened their combat capabilities, and determined the Germans' further successes; fourthly, the Germans secured complete control of the Donbas, the USSR’s most important economic region, which greatly weakened the Soviet economic, industrial and resources situation; and fifthly, the bulk of the Soviet strategic reserves trained in the first half of 1942 was exhausted, resulting in the absence of anything with which to parry or even deflect the subsequent German attacks.

The total Soviet losses in the 'Donbas Defensive Operation' are not known. The South Front suffered losses of 128,460 men killed, missing or taken prisoner, and 64,753 men wounded or taken ill, but the losses of the armies of the South-West Front’s left flank should be separated from the total losses of the front in the 'Voronezh-Voroshilovgrad Strategic Defensive Operation', but this is not possible: given the nature of the fighting, however, these losses must have been comparable to those of the South Front.

The German losses are not known.