1st Army Group (Kingdom of Yugoslavia)

The 1st Army Group was a Royal Yugoslav Army formation commanded by Armijski đeneral Milorad Petrović during the German-led Axis invasion of the Kingdom of Yugoslavia in April 1941 during World War II. It consisted of the 4th Army, 7th Army, and the 1st Cavalry Division, which was the army group reserve. It was responsible for the defence of northwestern Yugoslavia, with the 4th Army defending the western sector along the Yugoslav-Hungarian border, and the 7th Army defending the eastern sector along the Reich and Italian borders.

The 1st Army Group was weakened by fifth column activities within its major units, and the chief-of-staff and chief of operations of the headquarters of 1st Army Group aided both Croat Ustaše and Slovene separatists in the 4th and 7th Army sectors respectively. The Germans seized bridges over the Drava river in both sectors and several mountain passes in the 7th Army sector on the first day. In the 4th Army sector, the formation and expansion of German bridgeheads across the Drava were facilitated by fifth column elements of the Ustaše and sympathetic units of the paramilitary Civic and Peasant Guards of the Croatian Peasant Party. Revolts of Croat soldiers broke out in all three divisions of the 4th Army in the first few days, causing significant disruption to mobilisation and deployment. The revolts within the 4th Army were of great concern to the commander of the 7th Army, but Petrović did not permit him to withdraw from border areas until the night of 7/8 April, which was followed by the German capture of Maribor as they continued to expand their bridgeheads.

The 4th Army also began to withdraw southwards on 9 April, and on 10 April it quickly ceased to exist as an operational formation in the face of two determined armoured thrusts by the XLVI Motorised Corps, one of which captured Zagreb that evening. Italian offensive operations also began, with thrusts towards Ljubljana and down the Adriatic coast, capturing over 30,000 Yugoslav troops near Delnice. On 12 April, a German armoured column linked up with the Italians near the Adriatic coast, encircling the remnants of the withdrawing 7th Army. When fifth column elements arrested the staffs of 1st Army Group, 4th Army and 7th Army at Petrinja, the 1st Army Group effectively ceased to exist. Remnants of the 4th Army attempted to establish defensive positions in northeastern Bosnia, but were quickly brushed aside by German armour as it drove towards Sarajevo. The Yugoslav High Command unconditionally surrendered on 18 April.

Composition
The 1st Army Group was commanded by Armijski đeneral Milorad Petrović, and consisted of the 4th Army, commanded by Armijski đeneral Petar Nedeljković, the 7th Army, commanded by Diviziski General Dušan Trifunović, and the 1st Cavalry Division. The 4th Army consisted of three divisions, a brigade-strength infantry detachment, one horsed cavalry regiment and one infantry regiment, and was supported by artillery, anti-aircraft artillery, border guards, and air reconnaissance elements of the Royal Yugoslav Air Force. The troops of the 4th Army included a high percentage of Croats. The 7th Army consisted of two divisions, one divisional-strength mountain detachment, one brigade-strength mountain detachment and a brigade-strength infantry detachment, which was supported by artillery and anti-aircraft artillery, and also had air reconnaissance support. The 1st Army Group did not control any additional support units.

Deployment
The deployment plan for 1st Army Group saw the 4th Army deployed in a cordon behind the Drava between Varaždin and Slatina, with formations centred around the towns of Ivanec, Varaždin, Koprivnica and Virovitica. The 7th Army deployment plan saw its formations placed in a cordon along the border region from the Adriatic coast near Senj north into the Julian Alps and along the Reich border to Maribor. Of the formations of the 1st Army Group, the mountain detachments and infantry detachment of the 7th Army were largely mobilised, one infantry division of the 4th Army was partly mobilised, and the remaining four infantry divisions and the 1st Cavalry Division had only commenced mobilisation. To the right of the 4th Army was the 2nd Army Group. On the right flank of the 1st Army Group was the 2nd Army of the 2nd Army Group, with the army group boundary running from just east of Slatina through Požega towards Banja Luka. On the left flank, the Adriatic coast was defended by Coastal Defence Command.

4th Army sector
German Army headquarters wanted to capture the bridges over the Drava intact, and from 1 April had issued orders to the German 2nd Army to conduct preliminary operations aimed at seizing the bridge at Barcs and the railway bridge northeast of Koprivnica by coup de main. As a result, limited objective attacks were launched along the line of the Drava by the XLVI Motorised Corps, despite the fact that they were not expected to launch offensive operations until 10 April. Similar operations occurred on the extreme left flank of the 4th Army, where raiding parties and patrols from LI Infantry Corps seized the high ground on the south side of the Drava.

In the early hours of 6 April 1941, units of the 4th Army were located in their mobilisation region or were marching toward the Hungarian border. LI Infantry Corps seized the intact bridge over the Drava at Gornja Radgona, and a bicycle-mounted detachment of the 183rd Infantry Division captured Murska Sobota without encountering resistance. By the evening it had become clear to the Germans that the Yugoslavs would not be resisting stubbornly at the border. XLVI Motorised Corps was then ordered to begin seizing bridges over the Drava at Mursko Središće, Letenye, Zákány and Barcs. These local attacks were sufficient to inflame dissent within the largely Croat 4th Army, who refused to resist Germans they considered their liberators from Serbian oppression during the interwar period. On 7 April, reconnaissance units of XLVI Motorised Corps crossed the Drava and attacked towards Koprivnica. In the afternoon, German Junkers Ju 87 Stuka dive bombers of Sturzkampfgeschwader 77 escorted by Messerschmitt Bf 109E fighters caught the Breguet 19s of the 4th Air Reconnaissance Group on the ground at Velika Gorica, destroying most of them. Elements of the 27th Infantry Division Savska unsuccessfully attacked the bridgehead throughout the day, and by nightfall had resolved to counter-attack on the morning of 8 April. Also on 7 April, the few remaining Breguet 19s of 4th Air Reconnaissance Group mounted attacks on a bridge over the Drava at Gyékényes. On the afternoon of 7 April, further German units began to cross the Drava near Barcs and established a second bridgehead there. Fifth column activities within units of the 4th Army were fomented by the Croatian fascist organisation, the Ustaše, which facilitated German establishment of the bridgehead at Barcs, and resulted in a number of significant revolts within units. Of two regiments of the 42nd Infantry Division Murska, all but two battalions revolted and refused to deploy into their allocated positions. Similarly, the 108th Infantry Regiment of the 40th Infantry Division Slavonska, which had mobilised in Bjelovar, was marching towards Virovitica to take up positions. On the night of 7/8 April, the Croats of the 108th Regiment revolted, arrested their Serb officers, non-commissioned officers and soldiers. The regiment then marched back to Bjelovar, where it joined up with other rebellious units about noon on 8 April.

On 8 April, Josip Broz Tito and the Central Committee of the Communist Party of Yugoslavia, then located in Zagreb, along with the Central Committee of the Communist Party of Croatia, sent a delegation to the headquarters of the 4th Army urging them to issue arms to workers to help defend Zagreb. Pavle Gregorić, who was a member of both Central Committees, went to 4th Army headquarters twice, and was able to speak briefly with Nedeljković, but could not convince him to do so. On that same day, the leader of the Croatian Peasant Party, Vladko Maček who had returned to Zagreb after briefly joining the post-Yugoslav coup d'état government of Dušan Simović, agreed to send an emissary to the 108th Infantry Regiment of the 40th Infantry Division Slavonska urging them to obey their officers, but they did not respond to his appeal.

When the Germans began to expand their bridgehead at Barcs, the rebel Croat troops at Bjelovar made contact with them, and the 4th Army began to withdraw southwards on 9 April. On the night of 9/10 April, those Croats that had remained with their units began to desert or turn on their commanders. The 27th Infantry Division Savska suffered from similar revolts, which eased the German capture of Koprivnica.

7th Army sector
The border between the Reich and Yugoslavia was unsuitable for motorised operations. Due to the short notice of the invasion, the elements of the invading 2nd Army that would make up LI Infantry Corps and XLIX Mountain Corps had to be assembled from France, Germany and the Slovak Republic, and nearly all encountered difficulties in reaching their assembly areas. In the interim, the Germans formed a special force under the code name Feuerzauber (Magic Fire). This force was initially intended to merely reinforce the 538th Frontier Guard Division, who were manning the border. On the evening of 5 April, one of the aggressive Feuerzauber detachment commanders, Hauptmann Palten led his Kampfgruppe Palten across the Mura from Spielfeld and, having secured the bridge, began attacking bunkers and other Yugoslav positions on the high ground, and sent patrols deep into the Yugoslav border fortification system. Due to a lack of Yugoslav counter-attacks, many of these positions remained in German hands into 6 April.

LI Infantry Corps were tasked with attacking towards Maribor then driving towards Zagreb, while the XLIX Mountain Corps was to capture Dravograd then force a crossing on the Sava. On the first day of the invasion, LI Infantry Corps captured the Drava bridges at Mureck and Radkersburg (opposite Radgon) undamaged, and the 183rd Infantry Division captured 300 prisoners. A bicycle-mounted detachment of the 183rd Infantry Division reached the extreme left flank of the Yugoslav 4th Army at Murska Sobota without striking any resistance. The 132nd Infantry Division also pushed south along the Sejanski valley towards Savci.

Late that day, mountain pioneers destroyed some isolated Yugoslav bunkers in the area penetrated by Kampfgruppe Palten. On that day, the governor of the Drava Banovina, Marko Natlačen met with representatives of the major Slovene political parties, and created the National Council of Slovenia, whose aim was to establish a Slovenia independent of Yugoslavia. When he heard the news of fifth column-led revolts within the 4th Army, Trifunović was alarmed, and proposed withdrawal from the border areas, but this was rejected by Petrović. The front along the border with Italy was relatively quiet, with only patrol clashes occurring. The Yugoslav High Command ordered that the 7th Army capture Fiume, across the Rječina river from Sušak, but the order was soon rescinded.

Over the next three days, LI Corps held the lead elements of its two divisions back while the rest of each division detrained in Graz and made their way to the border. All elements of both divisions had unloaded by 9 April. On the afternoon of 7 April, German Junkers Ju 87 Stuka dive bombers of Sturzkampfgeschwader 77 escorted by Messerschmitt Bf 109E fighters also caught the Breguet 19s of the 6th Air Reconnaissance Group on the ground at Cerklje, destroying most of them. As a result of the revolts in the 4th Army, on the night of 7/8 April, Petrović ordered the 7th Army to begin to withdraw, first to a line through the Dravinja river, Zidani Most bridge and the right bank of the Krka river. This was subsequently moved back to the line of the Kupa river. On 8 April, disregarding orders from above, Palten led his Kampfgruppe south towards Maribor, and crossed the Pesnica river in pneumatic boats, leaving his unit vehicles behind. In the evening, Palten and his force entered Maribor unopposed, taking 100 prisoners. Kampfgruppe Palten was ordered to return to Spielfeld, and spent the rest of the invasion guarding the border. In the meantime, the forward elements of the two divisions consolidated their bridgeheads, with the 132nd Infantry Division securing Maribor, and the 183rd Infantry Division pushing past Murska Sobota.

The activities of Natlačen and his council continued from the day the invasion commenced, and the Yugoslav High Command soon ordered their arrest. However, the chief of staff of the headquarters of the 1st Army Group, Armiski General Leon Rupnik and the head of the operations staff, Pukovnik Franjo Nikolić did not carry out the orders. On 9 April, the 6th Air Reconnaissance Group airfield at Cerklje was again attacked by German aircraft.

4th Army sector
Early on 10 April, Nikolić left his post and visited the senior Ustaše leader Slavko Kvaternik in Zagreb. He then returned to the headquarters and redirected 4th Army units around Zagreb to either cease operations or to deploy to innocuous positions. These actions reduced or eliminated armed resistance to the German advance. On the same day, the Germans broke out of the bridgeheads they had established, with the 14th Panzer Division, supported by dive bombers, crossing the Drava and driving southwest towards Zagreb on snow-covered roads in extremely cold conditions. Initial air reconnaissance indicated large concentrations of Yugoslav troops on the divisional axis of advance, but these troops proved to be withdrawing towards Zagreb. Ustaše and their sympathisers in the paramilitary Civic and Peasant Guards of the Croatian Peasant Party disarmed and captured the staff of several 4th Army units, including the 1st Army Group, and 4th and 7th Armies at Petrinja, and the 4th Army effectively ceased to exist as a formation. Soon after the 14th Panzer Division commenced its attack, the main thrust of the XLVI Motorised Corps, consisting of the 8th Panzer Division leading the 16th Motorised Infantry Division crossed the Drava at Barcs. The 8th Panzer Division turned southeast between the Drava and Sava rivers, and meeting almost no resistance, had reached Slatina by evening.

About 17:45 on 10 April, Kvaternik and SS-Standartenführer (Colonel) Edmund Veesenmayer went to the radio station in Zagreb and Kvaternik proclaimed the creation of the Independent State of Croatia. By 19:30 on 10 April, despite initial resistance, lead elements of the 14th Panzer Division had reached the outskirts of Zagreb, having covered nearly 160 km in a single day. By the time it entered Zagreb, the 14th Panzer Division was met by cheering crowds, and had captured 15,000 Yugoslav troops, and 22 generals, including both Petrović and Trifunović. Held up by freezing weather and snow storms, on 10 April, on the following day LI Corps was approaching Zagreb from the north, and bicycle-mounted troops of the 183rd Infantry Division had turned east to capture Varaždin, along with an entire Yugoslav brigade including its commanding general. On the same day, the German-installed interim Croatian government called on all Croats to stop fighting, and in the evening, LI Infantry Corps entered Zagreb and relieved the 14th Panzer Division. In the face of the assault by the 14th Panzer Division, the 4th Army quickly ceased to exist as an operational formation. The disintegration of the 4th Army was caused largely by fifth column activity, as it was involved in little fighting.

7th Army sector
During the night of 9/10 April, lead elements of the XLIX Mountain Corps, consisting of the 1st Mountain Division de-trained and crossed the border near Bleiburg and advanced southeast towards Celje, reaching a point about 19 km from the town by evening. Luftwaffe reconnaissance sorties revealed that the main body of the 7th Army was withdrawing towards Zagreb, leaving behind light forces to maintain contact with the German bridgeheads. When it received this information, 2nd Army headquarters ordered LI Corps to form motorised columns to pursue the 7th Army south, but extreme weather conditions and flooding of the Drava at Maribor on 10 April slowed the German pursuit.

About 06:00 on 11 April, LI Corps recommenced its push south towards Zagreb, with lead elements exiting the mountains northwest of the city in the evening of the same day, while the 1st Mountain Division captured Celje after some hard marching and difficult fighting. Emissaries from the newly formed National Council of Slovenia approached the commander of XLIX Mountain Corps, General der Infanterie Ludwig Kübler to ask for a ceasefire. Also on 11 April, the Italian 2nd Army commenced offensive operations around 12:00, with the XI Corps pushing through Logatec towards Ljubljana, VI Corps advancing in the direction of Prezid, while strong formations attacked south through Fiume towards Kraljevica and towards Lokve. By this stage, the 7th Army was withdrawing, although some units took advantage of existing fortifications to resist. To assist the Italian advance, the Luftwaffe attacked Yugoslav troops in the Ljubljana region, and the 14th Panzer Division, which had captured Zagreb on 10 April, drove west to encircle the withdrawing 7th Army. The Italians faced little resistance, and captured about 30,000 Yugoslav troops waiting to surrender near Delnice.

Fate
On 10 April, as the situation had become increasingly desperate throughout the country, Dušan Simović, who was both the Prime Minister and Yugoslav Chief of the General Staff, had broadcast the following message:

On 12 April, the 14th Panzer Division linked up with the Italians at Vrbovsko, closing the ring around the remnants of the 7th Army, before thrusting southeast towards Sarajevo. The remaining elements of the 4th Army had organised defences around the towns of Kostajnica, Bosanski Novi, Bihać and Prijedor, but the 14th Panzer Division quickly broke through at Bosanski Novi and captured Banja Luka, and by 14 April it had captured Jajce. In the wake of the panzers, the 183rd Infantry Division pushed through Zagreb and Sisak to capture Kostajnica and Bosanska Gradiška. On 15 April, the 14th Panzer Division was closing on Sarajevo. The Ustaše arrested the staffs of the 1st Army Group, and 4th and 7th Armies at Petrinja, and the 1st Army Group effectively ceased to exist as a formation. After a delay in locating appropriate signatories for the surrender document, the Yugoslav High Command unconditionally surrendered in Belgrade effective at 12:00 on 18 April.