The 'Vienna Strategic Offensive Operation' was the Soviet operation by Marshal Sovetskogo Soyuza Fyedor I. Tolbukhin’s 3^rd Ukrainian Front to take Vienna, the capital of German-annexed Austria (16 March/15 April 1945).

As with all Soviet strategic offensives of this later period of the war, the 'Vienna Strategic Offensive Operation' fell into several parts, namely the 'Győr Offensive Operation' (13 March/4 April), the 'Veszprem Offensive Operation' (16/25 March), the 'Sopron-Baden Offensive Operation' (26 March/4 April), the 'Nagykanizsa-Körmend Offensive Operation' (26 March/15 April) and the 'Assault on Vienna Operation' (4/13 April).

The agreements reached by Premier Iosif Stalin and the Western Allies up to April 1945 were largely concerned with the countries' spheres of influence in much of eastern and central Europe in the aftermath of the war, but these agreements decided virtually nothing about the fate of Austria. Stalin thus decided to postpone the Soviet forces' offensive toward Berlin, for which the Soviets were ready as early as February, in order to secure both flanks for that offensive and also to take Austrian territory, all of which he saw as bargaining chips for negotiations with the Allied powers.

It was during the afternoon of 16 March that the Soviet counter-offensive began after after 'Frühlingserwachen' (ii) had been checked. The Soviet attacks started in conditions of snow and fog, and thus without major armoured or air support, against SS-Obergruppenführer under General der Waffen-SS Herbert Otto Gille’s IV SS Panzerkorps and the southern flank of Vezérezredes József Heszlényi’s Hungarian 3^rd Army on the front between Lake Velencze and Bicske. The original Soviet plan had been to send Marshal Sovetskogo Soyuza Rodion Ya. Malinovsky’s 2^nd Ukrainian Front toward Vienna in an advance straddling the Danube river, but in order to exploit the chance of trapping SS-Oberstgruppenführer und Generaloberst der Waffen-SS Josef Dietrich’s 6^th SS Panzerarmee in the area to the east of Lake Balaton, the main effort had been shifted farther to the south, and thus to the right flank of the 3^rd Ukrainian Front. The Soviet thrust was directed to the west and north-west along the axis linking Szekesfehervar, Varpalota, Papa, Sopron and Vienna. Inside this main thrust, the 2^nd Ukrainian Front was to attack along the Danube river in the direction of Győr.

On the second day of the Soviet offensive, the Hungarian 3^rd Army's flank collapsed and the Soviets drove through the Vertes mountains to the north of Mor. Neither of its major mobile formations, General Polkovnik Andrei G. Kravchenko’s 6^th Guards Tank Army and General Major Nikolai A. Pichugin’s 1^st Guards Cavalry-Mechanised Group (formerly the Cavalry-Mechanised Group 'Pliyev') had yet arrived to exploit the breakthrough, however, and General Otto Wöhler’s Heeresgruppe 'Süd' decided to 'postpone' (in fact cancel) its planned attack to the east of the Sarviz Canal and despatch SS-Obergruppenführer und General der Waffen-SS Hermann Priess’s I SS Panzerkorps 'Leibstandarte' into the area to the south-west of Szekesfehervar for a counterattack. By the end of the same day Heeresgruppe 'Süd' was also readying SS-Obergruppenführer und General der Waffen-SS Willi Bittrich’s II SS Panzerkorps to turn and move to the north. Malinovsky began turning his left-flank army to the north in the direction of Komarno behind the Hungarian 3^rd Army on 18 March, and on the same day General Leytenant Nikanor D. Zakhvatayev’s 4^th Guards Army and General Polkovnik Vasili V. Glagolev’s 9^th Guards Army of Tolbukhin’s 3^rd Ukrainian Front broke through Gille’s IV SS Panzerkorps between Mor and Lake Velencze. Tolbukhin was slow in taking advantage of the latter breakthrough as Kravchenko’s 6^th Guards Tank Army was not ready because it had been compelled to regroup to the south after the change in the Soviet overall plan. In the course of the same day Wöhler decided to attempt what could be described as a 'castling' manoeuvre: he instructed the 6^th SS Panzerarmee and its two corps to shift north into the sector between Lake Velencze and the Danube river, and gave General Hermann Balck’s 6^th Army command of the area lying between Lake Velencze and Lake Balaton. The 6^th SS Panzerarmee made its way out between the lakes, but the I SS Panzerkorps failed to secure a firm front in its new sector on the edge of the Bakony forest to the west of Varpalota.

On 20 March Kravchenko’s 6^th Guards Tank Army attacked between Varpalota and Szekesfehervar toward the tip of Lake Balaton. Adolf Hitler demanded that Szekesfehervar be held, which meant in effect that the 6^th Army had to remain in the area to the east of Lake Balaton. On the following day, with the exception of a tenuous corridor along the shore of the lake, the 6^th Army was encircled. Even so, Hitler refused to allow Szekesfehervar to be abandoned. The Oberkommando des Heeres explained that Hitler was concerned that if he did allow the loss of Szekesfehervar, the whole front would start to 'slide', which was in fact what was already happening. Wöhler replied that he could not risk another encirclement as the memory of what had taken place in Budapest was still too fresh and the armies were already infected with the Kessel ('cauldron', otherwise pocket) psychosis. Varpalota fell in the afternoon of the same day, and during the night which followed, regardless of Hitler’s demands, Szekesfehervar fell. For the next day the 6^th Army sought to extricate itself along the corridor, whose continued existence as all too problematical, between the lake and the Soviet forces. The army lost track of the IV SS Panzerkorps, and of the deserters who were seized some 75% were Waffen-SS soldiers.

The fact that the 6^th Army did in fact survive can be attributed primarily to the belated and somewhat uncertain start of Kravchenko’s 6^th Guards Tank Army. Thus by 23 March the 6^th Army had reached the area to the west of the lake, but was nonetheless still in great difficulties. During the day formations of the 3^rd Ukrainian Front took Veszprem, the key point and main road junction within the Bakony forest. On the same day, formations of the 2^nd Ukrainian Front split the bridgehead held by the Hungarian 3^rd Army to the west of Esztergom and forced this formation to fall back across the Danube river. Farther to the south, Generalfeldmarschall Maximilian Reichsfreiherr von Weichs’s Heeresgruppe 'F' in Yugoslavia evacuated its two bridgeheads across the Drava river. General Maximilian de Angelis’s 2^nd Panzerarmee, which was still attacking, advanced about 5 miles (8 km) in the area to the south of Lake Balaton, but this was a wholly pointless gain, and at the end of this day Hitler authorised Wöhler to take just one division from the 2^nd Panzerarmee.

During the day the Stavka had issued orders for the next phase of the Soviet offensive. Glagolev’s 9^th Guards Army and Kravchenko’s 6^th Guards Tank Army were to attack in the direction of Koszeg, General Leytenant Nikolai A. Gagen’s 26^th Army toward Szombathely, and General Polkovnik Sergei G. Trofimenko’s 27^th Army toward Zalaegerszeg.

At much the same time, the German high command received a very worrying report from Balck, who said that his men were not fighting as hard and as effectively as they should. Balck added that some of his men were saying the war was lost and did not wish to be among the last to die, all were afraid of being encircled, and the men’s loss of confidence and morale was also starting to become evident among higher command levels.

On 25 March the Soviets completed the breakthrough phase of their offensive as the 6^th Guards Tank Army emerged from the Bakony forest to the east of Papa. The 6^th SS Panzerarmee now held a front from Papa north to Komarno on the Danube river, but although relatively strong in numerical terms was revealing very severe operational limitations. From most senior to most junior, the Waffen-SS soldiers appeared to be unable to adjust to conditions in which they did not have the ample quantities of equipment and supplies and also the considerable time for the plotting of every move as had previously been the case. The 6^th Army had the impossible task of holding its right flank on Lake Balaton in order to shield the 2^nd Panzerarmee and of maintaining contact with the 6^th SS Panzerarmee on its left. In the area to the south of Papa, the gap between the two armies' flanks was 10 miles (16 km) wide, and Wöhler told Generaloberst Heinz Guderian, chief of the Oberkommando des Heeres’s staff, that he could divine no way to close it. Replying to Guderian’s demand that the 6^th Army's retreat be halted, Balck insisted that the crisis could in itself be mastered were it not for the soldiers' almost total loss of faith in the leadership, which according to Balck was the direct result of the defeats at Stalingrad and Budapest: for fear of encirclement and thus either death or imprisonment by the Soviets, the troops were not prepared even to try to hold.

Adding to the Germans' problems, the 2^nd Ukrainian Front began attacking across the Hron river on this same that day. On the following day, the 2^nd Ukrainian Front and 3^rd Ukrainian Front began what the Soviets later described as the pursuit. This word might have been adequate if the Germans were being routed or undertaking a planned retreat: the Soviets did not manage to compel the Germans into the former, and Hitler would not have permitted the latter. Thus a more apposite description would be an attempted active defence with wholly inadequate means and unsuitable objectives.

On 27 March the 6^th Guards Tank Army, 4^th Guards Army and 9^th Guards Army crossed to the Raab river on a broad front to the west of Koszeg. The very limited reinforcements reaching Heeresgruppe 'Süd' were to be employed, as a result of Hitler’s concern for the retention of the local oil-producing areas, for the German flanks, and were therefore allocated as two divisions to the 2^nd Panzerarmee and one division to General Hans Kreysing’s 8^th Army. After hearing that Hitler still demanded that Komarno be held for its oil refineries, Generalleutnant Heinz von Gyldenfeldt, the chief-of-staff of Heeresgruppe 'Süd', told the Oberkommando des Heeres to persuade Hitler to take a look at an aerial photograph: the area now comprised only bomb craters.

So far spared the worst of the Soviet offensive, the 2^nd Panzerarmee reported that it expected an attack imminently and that its Hungarian troops were deserting in large numbers, and therefore requested authorisation to fall back to the main defence line between Lake Balaton and the Drava river. When the army group forwarded the request with its endorsement, Guderian answered that to lay the matter before Hitler was a waste of time.

By a time two days later, the 6^th Guards Tank Army had crossed the Raab river between the flanks of the 6^th Army and 6^th SS Panzerarmee, and reached the Hungarian/Austrian border in the area of Koszeg and Szombathely. Hitler now permitted the two armies to pull back to the Austrian border defences, but ordered the two flanking armies to remain where they were. By the fall of night on 29 March the 8^th Army still had a very limited hold on Komarno, while the 2^nd Panzerarmee, which had come under Soviet attack for the first time during the day, had lost Nagybajom in the centre of its front in the area to the south of Lake Balaton and had taken command of the 6^th Army's right-flank corps at the southern tip of the lake to protect its deep flank and rear.

On 30 March the 6^th Guards Tank Army crossed the Hungarian/Austrian border and turned to the north in the direction of the corridor between the mountains to the west of Wiener Neustadt and Lake Neusiedler. On its right, the 9^th Guards Army and 4^th Guards Army began to wheel to the north-west in the direction of Vienna. Hitler demanded a counterattack to close the gap behind the tank army, but Wöhler replied that neither the 6^th Army nor the 6^th SS Panzerarmee had the slightest prospect even of starting let alone pressing any such counterattack. The army group would consider itself fortunate if the 6^th SS Panzerarmee was able to create, ahead of the Soviets, any kind of a front between Wiener Neustadt and the lake. Wöhler had despatched staff officers to assess the army group’s men: they had all reported that the soldiers were exhausted and their morale was low, and that to expect them to undertake a counterattack was futile. Moreover, the 6^th Army was in almost as much trouble on its right as on its left. It had broken away from the 2^nd Panzerarmee's flank, and the 27^th Army was pushing to the south.

At the end of the month the forces led by Tolbukhin and Malinovsky closed on Vienna. In the area to the north of the Danube river, the 2^nd Ukrainian Front advanced on Bratislava. The right flank of the 3^rd Ukrainian Front pushed into the narrows between the Danube river at Bratislava and Lake Neusiedler.

On 2 April the 6^th Guards Tank Army pushed past Wiener Neustadt toward Vienna. By this time the 2^nd Panzerarmee had retreated to the west of Nagykanizsa to a line in the heights that barely contained the oilfields. To aid in the defence of Vienna, Hitler despatched Generalmajor Oskar Audörsch’s 25^th Panzerdivision and Generalmajor Erich von Hassenstein’s Führer-Grenadierdivision, and on 3 April ordered Wöhler to attack the flanks of the Soviet breakthrough and cease his army group’s efforts to check the Soviet armoured spearheads with frontal attacks. After Wöhler had responded that his army group was in no condition to counterattack and had to place at least something in front of the Soviets so that they did not run rampant, Hitler recalled Generaloberst Dr Lothar Rendulic from Kurland, where he had commanded Heeresgruppe 'Kurland', to take over command of Heeresgruppe 'Süd'.

Arriving at the army group’s headquarters in the Alps to the south-west of St Poelten at about 24.00 on 7 April, Rendulic learned that the Soviets had penetrated into Vienna as far as the Guertelstrasse and were also on the Danube river to the west of the city. The 3^rd Ukrainian Front had moved the 46^th Army across the Danube river to the northern bank and was advancing beyond the Morava river to envelop Vienna on the north. The fighting in Vienna continued in Vienna until the afternoon of 13 April, but without any German attempt to make the city a major urban fortress of resistance. At the end of April’s second week, the 6^th SS Panzerarmee, 6^th Army and 2^nd Panzerarmee had an almost continuous front in the outlying Alps from a point to the west of St Poelten to the Drava river in the area to the east of Varazdin, and the loss of the Hungarian oilfields had gone almost unnoticed in the greater attention focussed on the battle for Vienna. After crossing the Hungarian/Austrian border, the Soviets relaxed their pressure against the two southern armies.

On 2 April 1945, a broadcast from Vienna denied that the Austrian capital had been declared an open city, and on the same day Soviet troops approached Vienna from the south after they had overrun Wiener Neustadt, Eisenstadt, Neunkirchen and Gloggnitz. The Soviets also overran Baden and Bratislava on 4 April. After arriving in the Vienna area, the armies of the 3^rd Ukrainian Front surrounded, besieged and attacked the city. Involved in this action were Zakhvatayev’s 4^th Guards Army, Kravchenko’s 6^th Guards Tank Army, Glagolev’s 9^th Guards Army and General Leytenant Mikhail S. Filippovsky’s 46^th Army.

The O5 Austrian resistance group, led by Carl Szokoll, wished to spare Vienna the likelihood of destruction in a prolonged battle, and therefore actively attempted to sabotage the German defence and aid the entry of the Soviet forces.

The only major German force facing the Soviet attack was Bittrich’s II SS Panzerkorps of the 6^th SS Panzerarmee, together with ad hoc forces made up of garrison and Flak units. Declared a defensive region, Vienna was entrusted to the command of General Rudolf von Bünau. The battle for the Austrian capital was characterised in some cases by fierce urban combat, but there were also parts of the city into which the Soviet forces advanced against little opposition. Defending Prater Park was Generalleutnant Rudolf Freiherr von Waldenfels’s 6^th Panzerdivision, along the south side of the city were SS-Standartenführer und Oberst der Waffen-SS Rudolf Lehmann’s (from 13 April SS-Standartenführer und Oberst de Waffen-SS Karl Kreutz’s) 2^nd SS Panzerdivision 'Das Reich' and SS-Brigadeführer und Generalmajor der Waffen-SS Hellmuth Becker’s 3^rd SS Panzerdivision 'Totenkopf', and in the north was von Hassenstein’s Führer-Grenadierdivision.

The Soviet forces delivered their assault into Vienna’s eastern and southern suburbs using the 4^th Guards Army and part of Glagolev’s 9^th Guards Army, but the German defence kept the Soviets out of the city’s southern suburbs until 7 April. However, after successfully achieving several footholds in the southern suburbs, the Soviets then moved into the western suburbs of the city on 8 April with Kravchenko’s 6^th Guards Tank Army and the bulk of the 9^th Guards Army. The western suburbs were especially important to the Soviets because they included Vienna’s main railway station. The Soviet success in the western suburbs was followed quickly by infiltration of the eastern and northern suburbs later the same day. In the area to the north of the Danube river, Filippovsky’s 46^th Army pushed westward through Vienna’s northern suburbs, and central Vienna was now cut off from the rest of Austria. By 9 April the Soviet troops began to infiltrate the centre of the city, but the street fighting continued for several days more.

On the night of 11 April the 4^th Guards Army stormed the Danube canals, with the XX Guards Corps and I Mechanised Corps moving toward the Reichsbrücke bridge. In a coup-de-main undertaking on 13 April the Danube Flotilla landed troops of the 80^th Guards Division and 7^th Guards Airborne Division on each side of the bridge, cutting demolition cables and securing the bridge. However, other important bridges were destroyed.

Vienna finally fell when the last defenders in the city surrendered on the same day. Bittrich’s II SS Panzer Corps pulled out to the west on the evening of April 13 to avoid encirclement, however, and on the same day the 46^th Army took Essling and the Danube Flotilla landed naval infantry up the river by Klosterneuburg.

While the street fighting was still intensifying in the southern and western suburbs of Vienna on April 8, other formations of the 3^rd Ukrainian Front bypassed Vienna altogether and advanced on Linz and Graz. By 15 April the 3^rd Ukrainian Front had pushed still farther into Austria, and the shattered remnants of the 6^th SS Panzerarmee were fleeing to the area between Vienna and Linz. Just behind the retreating Germans were elements of Glagolev’s 9^th Guards Army and the 46^th Army. Gagen’s 26^th Army and Trofimenko’s 27^th Army advanced toward the area to the north of Graz just behind Balck’s retreating 6^th Army. General Leytenant Mikhail N. Sharokhin’s 57^th Army and General Leytenant Vladimir D. Stoychev’s Bulgarian 1^st Army advanced toward the area lying to the south of Graz (near Maribor) just behind de Angelis’s retreating 2^nd Panzerarmee. None of these German armies capable of attempting anything but the temporary slowing of the advancing Soviet forces.

Some of Vienna’s finest buildings lay in ruins after the battle, there was no supply of water, electricity or gas, and bands of civilians, both foreigners and Austrians, plundered and assaulted the hapless residents in the absence of a police force. While the first wave Soviet assault forces generally behaved well, the second wave to arrive in the city was badly disciplined and as a result there was widespread looting, raping and killing for several weeks.

Like Bittrich, von Bünau left Vienna before its fall to avoid capture by the Soviets. From 16 April to the end of the war, von Bünau led the extemporised Generalkommando 'von Bünau', finally surrendering to US forces on VE-Day.

An Austrian politician, Karl Renner, established a provisional government in Vienna in April 1945 with the tacit approval of the Soviets, and declared Austria’s secession from the Third Reich.

In the second half of the month, the weight of the Soviet offensive shifted into the area to the north of the Danube river. The 1^st Guards Cavalry-Mechanised Group attacked across the Morava river toward Brno, and General Andrei I. Eremenko’s 4^th Ukrainian Front moved toward Olomouc against the bulging right flank of Generaloberst Georg-Hans Reinhardt’s Heeresgruppe 'Mitte'. Hitler instructed Heeresgruppe 'Süd' to retake the small Austrian oilfield at Zistersdorf, some 25 miles (40 km) to the north of Vienna, but no such effort could be made.