The 'Carpathian-Uzhgorod Offensive Operation' was a Soviet undertaking by General Polkovnik (from 26 October General) Ivan Ye. Petrov’s 4^th Ukrainian Front within the context of the 'East Carpathian Strategic Offensive Operation', and in parallel with the 'Carpathian-Dukla Offensive Operation', to defeat Generaloberst Gotthard Heinrici’s Armeegruppe 'Heinrici' and to complete the liberation of Transcarpathian Ukraine (9 September/28 October 1944).

On 29 August, there began the Slovak National Rising against the pro-Nazi government of German-occupied Slovakia. Given the fact that the rebels' forces were numerically and technically far inferior to those of the Germans, however, the Germans were quickly able to gain the upper hand if not immediately crush the rising, and on 31 August the rebels requested the aid of the USSR, which had major forces on the other side of the Carpathians from the area held by the rising. The Soviet supreme command quickly appreciated the political as well as military advantages of providing such assistance, and on 2 September ordered an offensive by the 38^th Army on the left wing of Marshal Sovetskogo Soyuza Ivan S. Konev’s 1^st Ukrainian Front and by Petrov’s 4^th Ukrainian Front. At much the same time, Admiral Miklós Horthy de Nagybánya, the dictator of Hungary, which ruled Transcarpathia and was watching with great apprehension the advance of Soviet troops toward his country, was seeking a way to extract Hungary from the war as an ally of Germany.

The 4^th Ukrainian Front was ordered to support the 1^st Ukrainian Front, which had been allocated the task of delivering the 'Carpathian-Dukla Offensive Operation' which was the main blow of the 'East Carpathian Strategic Offensive Operation'. The 4^th Ukrainian Front was to cross the eastern part of the Carpathian mountains and take the area of Mukachevo, Uzhgorod and Chop. As this undertaking had been assigned to the 4^th Ukrainian Front quite suddenly, the operation’s plan was reported by Petrov to the Soviet supreme Command only on 13 September after his staff had amended the general plan provided by the Stavka and counting on the combination of surprise and the disruption on the German forces' rear areas caused by the activities of the Slovak troops and partisan detachments.

By the beginning of the 'Carpathian-Uzhgorod Offensive Operation', the 4^th Ukrainian Front held the line extending between Sanok and Krasnoilsk via Skole, and its strength of 153,00 men, 184 tanks and self-propelled guns and 3,100 pieces of artillery and mortars was deployed in General Polkovnik Andrei A. Grechko’s 1^st Guards Army, General Leytenant Yevgeni P. Zhuravlev’s 18^th Army and General Major Anton I. Gastilovich’s XVII Guards Corps. Air support was provided by General Leytenant Vasili N. Zhdanov’s 8^th Air Army.

The Soviets were opposed by part of Generaloberst Gotthard Heinrici’s 1^st Panzerarmee and Vezérezredes Béla Dálnoki Miklós (from 16 October Altábornagy László Dezsöo’s) Hungarian 1^st Army, which together constituted Heinrici’s Armeegruppe 'Heinrici'. This grouping possessed 106,000 men and 1,790 pieces of artillery and mortars, and occupied a strong defensive position of some depth.

On 9 September, the 1^st Guards Army moved forward from the area of Sanok and Zaluzh toward Comancha and the Russkiy pass. Overcoming determined resistance, by 14 September the 1^st Guards Army had broken through the defences and created a gap 18.5 miles (30 km) wide and advanced to a depth of 9.33 miles (15 km). On 20 September, the Soviet formations entered Slovakia, and by this time the Germans were so concerned that they rapidly reinforced their forces with another eight divisions. Thus strengthened, the Germans managed to slow almost to a halt the Soviet progress, and the fighting then became protracted.

Meanwhile, in the 18^th Army’s offensive zone, Soviet troops were able to break through the German defences and advance toward the Uzhok and Verecke passes. On the front’s southern flank, the XVII Guards Corps was advancing from the Delyatin area toward Yasin. Alternating the offensive efforts of both armies, Petrov was able to achieve a slow but steady advance, and by 30 September both armies had reached the main Carpathian mountain range after advances of 25 miles (40 km).

By 18 October, the 4^th Ukrainian Front had seized the Russkiy, Uzhok, Verecke, Yablonitsky and other passes, and continued to advance down the south-western and southern slopes of the eastern part of the Carpathian mountains. The offensive’s main success was in fact attributable largely the actions of neighbouring fronts, most especially the 2^nd Ukrainian Front which, in the course of the 'Debrecen Offensive Operation', occupied the part of the Hungarian plain adjacent to the Carpathian mountains, reached the region to the south-west of Uzhgorod and threatened to encircle the forces defending in the eastern part of the Carpathian mountains. Under this threat, Armeegruppe 'Heinrici' began to retreat.

At this stage of the operation, Petrov was able to organise the pursuit of the withdrawing German and Hungarian and thwart their planned withdrawal. After defeating the German and Hungarian rearguards, the 4^th Ukrainian Front’s forces broke into the valley of the Tisza river and rapidly advanced to the east as much as some 60 to 90 miles (100 to 150 km). On 26 October, the Soviets took Mukachevo on 27 October Uzhgorod and on 29 October Chop. The Soviet offensive came to a halt to the west of the line between Gmina Komańcza and Snina as a result of he troops' exhaustion and the defeat of the Slovak National Rising.

During the operation, the 4^th Ukrainian Front had therefore failed to achieve fully the tasks which had been assigned to it. Even so, it had been able to overcome some of the most difficult parts of the Carpathian mountains and to inflict heavy losses on the German and Hungarian forces. The Hungarian 1^st Army suffered most heavily and was effectively and completely defeated. Transcarpathian Ukraine had been liberate and part of Slovakia taken, in he process covering the northern flank of the 'Budapest Strategic Offensive Operation'.

According to Soviet estimates, the German and Hungarian forces had lost some 60,000 men killed and 28,000 men taken prisoner. Soviet and Russian data on the Soviet losses are somewhat contradictory: one source admits the loss of 13,500 men killed or missing, and 50,618 men wounded or taken ill, while another admits the loss of 41,500 men killed and wounded, 1,800 men missing and 13,500 men taken ill or frost-bitten.