This was a Soviet part of the third phase of the ‘Belorussian Strategic Offensive Operation’ better known as ‘Bagration’ (28 July/28 August 1944).
The undertaking was the responsibility of General Ivan D. Chernyakhovsky’s 3rd Belorussian Front, which was tasked with the destruction of the German concentration on the western bank of the Niemen river, the capture of Kaunas, and the advance to the border of East Prussia.
After completing the ‘Vilnyus Offensive Operation’, the major formations of the 3rd Belorussian Front 1 were engaged in intense fighting with German forces on the approaches to the Niemen river during the second half of July, and were preparing for the continuation of the offensive. They were resisted by formations and units of Generaloberst Georg-Hans Reinhardt’s 3rd Panzerarmee and General Kurt von Tippelskirch’s 4th Army within Generalfeldmarschall Walter Model’s Heeresgruppe ‘Mitte’.
By 18 July the increased pressure of the Soviet offensives against the adjacent flanks of Model’s Heeresgruppe 'Mitte' and Generaloberst Johannes Friessner’s Heersgruppe 'Nord' was being felt more dangerously, and it was at this time that a captured Soviet officer informed his interrogators that he had seen the 2nd Guards Army of the 1st Baltic Front moving to the west in the direction of the 3rd Panzerarmee's northern flank. The 5th Guards Tank Army, with the 33rd Army close behind it, had closed up to the 3rd Panzerarmee's to the east of Kaunas and along the Niemen river to the south of the city. Possessing only one weak Panzer division and four infantry divisions with which to oppose 18 infantry divisions, three tank corps, one mechanised corps and three independent tank brigades, Reinhardt reported that he saw no chance of restoring contact with Heeresgruppe 'Nord' and asked for authorisation to pull his northern flank back far enough to create a strong front around Kaunas. After returning from a conference with Adolf Hitler, Model told Reinhardt that the 3rd Panzerarmee would have to remain where it was, and that Heeresgruppe 'Nord' would close the gap, though he made no suggestion as to how the army group might do so. Model also promised Reinhardt a reinforcement in the form of Generalmajor Wilhelm Schmalz’s 1st Fallschirmpanzerdivision 'Hermann Göring'.
During the next three days, as the 5th Tank Army increased its threat to Kaunas by establishing several bridgeheads over the Niemen river, the 2nd Guards Army moved to the west into the Baltic gap and began driving the 3rd Panzerarmee's flank to the south. By 22 July the flank division, trying to hold off six guards infantry divisions, was beginning to disintegrate, and the gap had opened to a width of 36 miles (58 km). In the course of the same day the 2nd Guards Army’s advance elements reached Panevezhis, some 40 miles (65 km) behind the 3rd Panzerarmee's front.
By this time the 3rd Panzerarmee had been whittled away to an effective combat strength of only 13,850 men, but Model again refused a request for retreat. As far as reinforcements were concerned, Model informed Reinhardt, the 3rd Panzerarmee would have to survive on its own for two or three more days.
General Paul Laux’s 16th Army had meanwhile completed its withdrawal into the 'Litauen-Stellung' position between Ostrov and Kraslava on 19 July, but had not been able to halt the Soviets along this line. On 22 July Friessner ordered the army to fall back another 5 to 10 miles (8 to 16 km), which meant abandoning its northern anchor point at Pskov. Friessner told Hitler that there was no other way of holding the army together, that the new line also would not hold, and that the army group would then have to fall back once again. Soon, Friessner added, the front would lose its connection with the line in the area of Lakes Pskov and Peipus, and a retreat behins the line of the Dvina river would then become a matter of survival for the entire army group.
On 20 July there was the 'July plot' attempt to kill Hitler at his East Prussian headquarters: the detonation of a briefcase bomb wounded all 19 officers at the afternoon situation conference, three of them fatally, and had demolished the building in which the meeting was being held, but Hitler escaped with minor burns, bruises and an ear injury. In the next few hours, there emerged the first details of a major conspiracy against Hitler, this being centred on the army and reaching into the highest command echelons, especially the army general staff. The conspiracy was quickly destroyed, and before the day was out Hitler had placed new men in a number of key posts. So far as the Eastern Front was concerned, the most significant change was the appointment of Generaloberst Heinz Guderian, the inspector general of armoured troops, as the Oberkommando des Heeres’s as acting chief-of-staff. Guderian received this appointment only because Hitler’s first choice, General Walter Buhle, had been wounded in the assassination attempt. Though still not in Hitler’s good books, Guderian was on 20 July possibly the only general in the Oberkommando des Heeres not under direct suspicion. Guderian was the officer who, in Berlin on the afternoon of the assassination attempt, had turned back the tank battalion drawn up to take the SS headquarters. He had, moreover, lately been full of ideas for winning the war, and he had not attempted to hide his low opinion of the senior leadership on the Eastern Front since his dismissal from field command on 26 December 1941.
Guderian now acted with alacrity to give fresh evidence of his loyalty to Hitler and to dissociate himself from his predecessors. In an order to all general staff officers, he demanded a full and public commitment to the Nazi part line on political questions, and that those who could not comply were to ask for removal from the general staff.
On his first day in his new post Guderian demonstrated how he proposed to supervise the war on the Eastern Front. When Generalmajor Oldwig von Natzmer, the chief-of-staff of Heeresgruppe 'Nord' only since 19 July, informed Guderian that Friessner was convinced the course Hitler was following would lose him the Baltic states, as well as the 16th Army and 18th Army, Guderian dismissed the statement with the sneering comment that he expected 'Friessner will be man enough to give the necessary orders [to surrender] in the event of a catastrophe.'
After Friessner submitted his 22 July report, his tenure of command over Heeresgruppe 'Nord' was in effect over. At Guderian’s instigation, on the following day Friessner and Schörner, the latter commanding Heeresgruppe 'Süd', exchanged places, and Guderian told Model that he was confident Schörner would restore the position of Heeresgruppe 'Nord'. The new commander reached Heeresgruppe 'Nord' with orders from Hitler to take command over all combat forces of the three Wehrmacht branches, the Waffen-SS, and the party and civil administration of the Baltic states. However, this unusual combination or power amounted to little in practical terms, for its placed at Schörner’s disposal only a few thousand men who could be committed in the gap on the army group’s southern flank.
Concerned about the threatening developments of 22 July on his front and flanks, on 23 July Model predicted that the Russians would strike via Lwów to the San river, drive past Lublin to Warsaw, encircle Generaloberst Walter Weiss’s 2nd Army at Brest, advance toward East Prussia across the Białystok-Grodno line and by way of Kaunas, and push past the army group’s left flank via Šiauliai to Memel or Riga. During the day Model’s concern, particularly for his southern flank, grew to alarm as the Soviets moved to the north rapidly between the Vistula and Bug river toward Siedlce, which was on the main road junction between Warsaw and Brest-Litovsk. In the late afternoon, after several of his reports had gone unanswered, Model called to tell the operations branch of the Oberkommando des Heeres that there was no alternative to a the line of the Vistula and San rivers. Model was then told that Guderian intended to set a different objective. The army group’s chief-of-staff later spoke to Guderian, who quickly took up a proposal to create a strong armoured force around Siedlce but would not entertain any suggestion of abandoning any of the most threatened points, and demanded that offensive action be taken immediately.
Before the advent of light on the following day, Guderian had completed a directive which was issued over Hitler’s signature. Heeresgruppe 'Nordukraine' and Heeresgruppe 'Südukraine' were to halt along the lines they currently held, and to start attacking to close the gaps. Heeresgruppe 'Mitte' was to establish a solid front on the line linking Kaunas, Białystok and Brest-Litovsk, and to assemble on both its flanks strong forces with which to strike to the north and to the south to restore contact with the adjacent army groups. All three army groups were promised reinforcements.
After reading the directive, Model’s chief-of-staff told the head of the Oberkommando des Heeres’s operations staff that it would be seven days before the army groups would get any sizeable reinforcements, and in that time the situation could alter rapidly and sizeably.
Such was indeed the case, for during the last week of July the Soviet armies drove to the west through the shattered German front. On 24 July Generaloberst Erhard Raus’s 1st Panzerarmee still held Lwów and its front to the south, but behind the Panzer army’s flank, 50 miles (80 km) to the west of Lwów, the 1st Tank Army, 3rd Guards Tank Army and the Cavalry-Mechanised Group 'Baranov' had four tank and mechanised corps which were closing to the San river along the stretch between Jarosław and Przemyśl. On the same day General Walther Nehring’s 4th Panzerarmee fell back a distance of some 25 miles (40 km) to a 40-mile (65-km) front on the Wieprz river to the south-east of Lublin, but on each of its flanks the Soviets ripped open the front for a distance of 65 miles (105 km) in the south and 55 miles (90 km) in the north. The 2nd Army had drawn its three right-flank corps back to form a horizontal V with its apex at Brest-Litovsk. Behind the army a spearhead of the 2nd Tank Army had reached the outskirts of Siedlce by the fall of night on 24 July, and during the day the 47th and 70th Armies had turned in against the south flank.
On 24 July, in order to defend Siedlce, Warsaw and the Vistula river as far to the south as south to Puławy, Model returned the headquarters of General Nikolaus von Vormann’s 9th Army to the front and allocated to it the 1st Fallschirmpanzerdivision 'Hermann Göring', SS-Brigadeführer und Generalmajor Helmuth Becker’s 3rd SS Panzerdivision 'Totenkopf' and two infantry divisions, of which the last three were still in transit. From the long columns streaming to the west across the Vistula river, the army began to comb out whatever troops it could. In Warsaw it expected an uprising at any moment.
Near the end of July, according to Soviet estimates the German formations concentrated in the area of Kaunas and faced with the 'Kaunas Offensive Operation', included elements of two Panzer divisions, 10 infantry divisions, two infantry brigades and 30 separate regiments and battalions. The Stavka tasked the 3rd Belorussian Front with pressing home the attack on the Kaunas axis no later than 1/2 August by means of concentric assaults by the 39th Army together with the 5th Guards Tank Army from the north, and the 5th and 33rd Armies from the south to occupy Kaunas, which was the most important defensive position on the approaches to East Prussia. The plan demanded that the Soviet forces advance to the borders of East Prussia by 10 August before assuming a temporary defensive stance as preparations were completed for the advance into East Prussia. As with the parallel defence against the Białystok farther to the south, Model concentrated on a holding and delaying action using the few units available to him.
The German order of battle for mid-July revealed units from a large number of divisions in the area, but many of these were merely fragments which had escaped from the encirclement of the bulk of Heeresgruppe ‘Mitte’ in the previous phases of ‘Bagration’. Thus the 3rd Panzerarmee comprised only Oberst Hermann-Heinrich Behrend’s Korpsabteilung ‘G’ (remnants of Generalmajor Herbert Michaelis’s 95th Division, Generalmajor Hans Hahne’s 197th Division and Generalleutnant Albrecht Wüstenhagen’s 256th Division which had escaped the previous phase of ‘Bagration’), General Gerhard Matzky’s XXVI Corps (parts of Oberst Hans-Otto von Bernuth’s 6th Panzerdivision and other divisions), General Rolf Wuthmann’s vestigial IX Corps, while the northern part of the Tippelskirch’s (from 18 July General Friedrich Hossbach’s) 4th Army comprised General Dietrich von Saucken’s reconstructed XXXIX Panzerkorps and Generalmajor Gerhard Schmidhuber’s 7th Panzerdivision.
Chernyakhovsky committed his forces to the offensive on 28 July, and by the end of the following day these had advanced between 3 and 10.5 miles (5 and 17 km). By 30 July the German resistance on the approaches to the Niemen river had been broken. In the 33rd Army’s sector, Major General Aleksei S. Burdeiny’s II Guards Tank Corps was introduced into the breakthrough, and its rapid advance to Vilkaviškis threatened the German forces to the east of Kaunas with encirclement, prompting a German retreat. Exploiting the success of the II Guards Tank Corps, the troops of the 33rd Army entered and secured Vilkaviškis and the railway junction of Mariampolė on 31 July. Troops of the 5th Army broke into Kaunas and on the morning of 1 August took control of the city. Toward the beginning of August the forces of the 3rd Belorussian Front advanced up to 30 miles (50 km) and subsequently enlarged the breakthrough to 145 miles (230 km), taking more than 900 villages, townships, towns and small cities.
During August, the 3rd Panzerarmee, commanded since 15 August by Generaloberst Erhard Raus as Reinhardt succeeded Model in command of Heeresgruppe ‘Mitte’, was reinforced and mounted a counter-offensive on the 3rd Belorussian Front’s northern flank in ‘Doppelkopf’. German troops also delivered a series of strong counterattacks south-west and west of Kaunas. Having countered these, the 3rd Belorussian Front’s formations moved some 18.5 to 31 miles (30 to 50 km) farther and advanced toward the German prepared fortified positions on the line to the east of Raseiniai and Kybartai-Suwalki.
On the orders of the Stavka, from 29 August the 3rd Belorussian Front went over to the defensive, but as a result of the Kaunas operation the forces of the 3rd Belorussian Front had reached the eastern borders of East Prussia.