The 'Arpad-Linie' was a German and Hungarian defence line for Altábornagy Béla Miklós von Dalnoki’s Hungarian 1^st Army in the northern foothills of the eastern Carpathian mountains, extending in a south-easterly direction from south-eastern Poland through Slovakia and northern Romania into Ukraine (8 September/6 October 1944).

The need for the Soviets to break though the north-west of this line and debouch into the Slovak and Hungarian plain resulted in the 'Carpatho-Dukla Offensive Operation', and was centred on the Dukla pass. This is a strategically significant mountain pass in the Laborec highlands of the Outer Eastern Carpathian mountains on the border between Poland and Slovakia, and close to the western border of Ukraine. At an altitude of 1,645 ft (502 m), the Dukla pass is the lowest crossing of the main range of the Carpathian mountains, and is located to the south of Dukla in Poland and to the north-east of Presov in Slovakia.

The 'Battle of the Dukla Pass' that followed was a bitterly fought undertaking in which the German resistance was much stronger than the Soviets had anticipated, and as a result the fighting lasted from 8 September to 6 October before the Soviets managed to break through the pass, and German forces ended their major resistance in the region only around 10 October. An anticipated five-day advance to Presov thus became a 50-day inching just to Svidnik, with more than 70,000 casualties on each side, and Presov remained beyond the grasp of General Major Ludvík Svoboda’s Czechoslovak I Corps, attached to Marshal Sovetskogo Soyuza Ivan S. Konev’s 1^st Ukrainian Front, for four months. As such, the battle was among the bloodiest of all Eastern Front battles.

During the summer of 1944 many Slovaks rebelled against the Germans in the Slovak National Rising and called for Soviet assistance. On 31 August Konev was instructed to develop a plan for an offensive to destroy the German forces in Slovakia. The plan was to push through the old Slovak/Polish border in the Carpathian mountains via the Dukla pass near Svidnik and thus to penetrate into Slovakia proper.

Meanwhile the Germans had fortified the region, forming the Karpatenfestung (otherwise the 'Árpád-Linie'). Konev’s plan was posited on the concept of the Soviet forces crossing through the pass to take Presov within five days. To hold their positions, the Germans and Hungarians had 100,000 men, 2,000 pieces of artillery and about 350 armoured fighting vehicles in Generaloberst Gotthard Heinrici’s Armeegruppe 'Heinrici' (Heinrici’s own 1^st Panzerarmee and elements of the Hungarian 1^st Army). The Soviets had between 120,000 and 150,000 men as well as the 16,700 Czechoslovaks of the Czechoslovak I Corps, 1,517 pieces of artillery, 1,724 mortars and 1,000 armoured fighting vehicles of General Polkovnik Kirill S. Moskalenko’s 38^th Army of the 1^st Ukrainian Front and General Leytenant Andrei A. Grechko’s 1^st Guards Army of General Polkovnik Ivan Ye. Petrov’s 4^th Ukrainian Front.

The Soviet operation started on 8 September, and took three days to take Krosno. One of the most savage battles in the pass took place on and around Hill 534 to the north-west of the town of Dukla: This phase of the operation lasted from 10 to 20 September, and during that period the control of the hill changed more than 20 times. The Soviets finally took the town of Dukla on 21 September, and captured the area of the former Czechoslovak border, which had been heavily fortified by the Germans, on 6 October. Thus it took the Soviets almost a month to reach Slovakia.

Yet the operation did not end when the Soviets had forced the pass, for the fighting then moved into the eastern part of Slovakia as the Soviets attempted to outflank and push back the German forces, still strong and fighting from many fortified positions. To the south of the pass and directly to the west of the village of Dobraslava lies an area which came to be known as the 'Valley of Death' for the severity of the fighting that took place here. Soviet and German armour clashed in a comparatively small but extremely savage tank battle.

The Soviet and Czechoslovak forces entered Svidnik only on 28 October, and a major German fortified position near the pass, Hill 532, was taken only on 25 November. The slow nature of the Soviet advance meant that the Slovak National Rising had been effectively crushed before Soviet units entered Slovakia: this resulted not only from the determination of the German resistance, but also the fact that the Slovak insurgent forces failed to secure the southern side of the pass as planned by Slovak and Soviet commanders during early preparations.

It is hard to determine the battle’s casualty levels, especially those of the Germans who are believed to have lost anywhere between 20,000 and 70,000 men killed, wounded and taken prisoner. The Soviets lost between 20,000 and 21,000 men killed, and between 60,000 and 110,000 men wounded or missing, while the Czechoslovaks suffered 8,500 casualties.