The 'Assault on Vienna Operation' was the Soviet seizure of Vienna, the capital of German-annexed Austria, as the culmination of the 'Vienna Strategic Offensive Operation' (5/13 April 1945).
At this time was defended by eight Panzer and Panzergrenadier divisions, one infantry division and as many as 15 separate infantry battalions of Generaloberst Dr Lothar Rendulic’s Heeresgruppe 'Ostmark'. On the approaches to and within the city itself, the Germans had readied large numbers of field fortifications and other defensive structures including, round the more vulnerable areas of the city’s perimeter, anti-tank ditches and other anti-tank and anti-personnel obstacles and barriers, the streets were blocked by barricades and rubble, and many buildings had been developed into positions armed with machine guns and other closer-combat weapons. The Germans had thus attempted to create an impregnable fortress in Vienna as the German political and military leadership attached great importance to the retention of Vienna and its economic region. On 6 April, Hitler recorded that 'The oilfield in the Vienna region is of decisive importance for the further conduct of the war.'
Vienna was the last significant bastion of the German defences on the edge of Germany’s southern regions. As a result, the fighting for the city was notably stubborn. According to the plan outlined by the Soviet supreme command, the 'liberation' of Vienna was to be effected by the right-wing forces of Marshal Sovetskogo Soyuza Fyedor I. Tolbukhin’s 3rd Ukrainian Front (4th Army, 9th Guards Army and 6th Guards Tank Army, the I Guards Mechanised Corps and the XVIII Tank Corps) and the left-wing forces of Marshal Sovetskogo Soyuza Rodion Ya. Malinovsky’s 2nd Ukrainian Front (46th Army, XIII Tank Corps and II Guards Mechanised Corps). Air support was provided by elements of units of General Polkovnik Sergei K. Goryunov’s 5th Air Army and General Polkovnik Vladimir A. Sudets’s 17th Air Army. In the battle for Vienna, use was also made of the vessels of Vitse Admiral Georgi N. Kholostyakov’s Danube Military Flotilla.
Wishing to preserve the city and its host of historical monuments, and also to prevent unnecessary loss of life, on 6 April Tolbukhin appealed to the inhabitants of Vienna not to flee, to make every effort they could to prevent the Germans from destroying the city, and to aid the Soviet forces. Only a very limited number of the city’s inhabitants responded to the call.
On the morning of 6 April, the 4th Army and 9th Guards Army attacked from east and south. At the same time, the 6th Guards Tank Army bypassed the city from the west as the Soviet attempted to sever all the routes by which the retreating Germans could make an attempt to escape to the west. Soviet armoured forces crossed the area of the Vienna Woods and, despite the difficulty of the terrain and the determination of the German defenders, reached the Danube river on 7 April, thereby cutting the German escape routes. The city was now surrounded on three sides.
Formations of the 3rd Ukrainian Front fought for every quarter of the city and steadily overcome the German defensive positions built into house. A group of reconnaissance troops braved intense German fire to clear the charges which had been placed for the demolition of the Reichsbrücke. Clearing one one block after another, the Soviet troops dismembered the German defences and continued to destroy them. By 10 April, Soviet troops advancing from the south and east had linked with the units storming the city centre. The German garrison was steadily squeezed from the south and east by the 4th Army, and from the south-west and west by the 9th Guards Army and 6th Guards Tank Army. Even so, the Germans entertained no question of surrender. On the night of 11 April, the 4th Guards Army began to cross the Danube Canal, and two days later the German resistance had been broken.
As some of their elements completed the clearance of the city of Vienna, other elements reached the St Pölten line and entrenched themselves farther to the south. The troops of the left wing of the 3rd Ukrainian Front continued their offensive in the general direction of Graz.