On April 2, 1945, Vienna Radio denied that the Austrian capital has been declared an open city.
On the same day, Soviet troops approached Vienna from the south after they overran Wiener Neustadt, Eisenstadt, Neunkirchen, and Gloggnitz. Baden and Bratislava were overrun on April 4.
After arriving in the Vienna area, the armies of the Soviet 3rd Ukrainian Front surrounded, besieged, and attacked the city. Involved in this action were the Soviet 4th Guards Army, the Soviet 6th Guards Tank Army, the Soviet 9th Guards Army, and the Soviet 46th Army. The "O-5 Resistance Group," Austrians led by Carl Szokoll wanting to spare Vienna destruction, actively attempted to sabotage the German defenses and to aid the entry of the Red Army.
The only major German force facing the Soviet attackers was the German II SS Panzer Corps of the 6th SS Panzer Army, along with ad-hoc forces made up of garrison and anti-aircraft units. Declared a defensive region, Vienna's defense was commanded by General Rudolf von Bünau, with the II SS Panzer Corps units under the command of SS General Wilhelm Bittrich.
The battle for the Austrian capital was characterized in some cases by fierce urban combat, but there were also parts of the city the Soviets advanced into with little opposition. Defending in the Prater Park was the 6th Panzer Division, along the south side of the city were the 2nd and 3rd SS Panzer Divisions, and in the north was the Führer-Grenadier Division. The Soviets assaulted into Vienna's eastern and southern suburbs with the 4th Guards Army and part of the 9th Guards Army. The German defenders kept the Soviets out of the city’s southern suburbs until April 7. However, after successfully achieving several footholds in the southern suburbs, the Soviets then moved into the western suburbs of the city on April 8 with the 6th Guards Tank Army and the bulk of the 9th 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. North of the Danube River, the 46th Army pushed westward through Vienna's northern suburbs. Central Vienna was now cut off from the rest of Austria.
By April 9, the Soviet troops began to infiltrate the center of the city, but the street fighting continued for several days more. On the night of April 11, the 4th Guards Army stormed the Danube canals, with the 20th Guards Rifle Corps and 1st Mechanized Corps moving on the Reichsbrücke Bridge. In a coup de main on April 13, the Danube Flotilla landed troops of the 80th Guards Rifle Division and 7th Guards Airborne Division on both sides 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, however, pulled out to the west on the evening of April 13 to avoid encirclement. The same day, the 46th 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 troops of the 3rd Ukrainian Front by-passed Vienna altogether and advanced on Linz and Graz.
After arriving in the Vienna area, the armies of the Soviet 3rd Ukrainian Front surrounded, besieged, and attacked the city. Involved in this action were the Soviet 4th Guards Army, the Soviet 6th Guards Tank Army, the Soviet 9th Guards Army, and the Soviet 46th Army. The O-5, a group of Austrians led by Carl Szokoll and wanting to spare Vienna destruction, actively attempted to sabotage the German defense and aid the entry of the Red Army.