4th Army (Kingdom of Yugoslavia)

The 4th Army was a Royal Yugoslav Army formation commanded by Armiski đeneral Petar Nedeljković during the German-led Axis invasion of the Kingdom of Yugoslavia in April 1941 during World War II. It consisted of three divisions, a brigade-strength infantry detachment, one horsed cavalry regiment and one infantry regiment. It formed part of the 1st Army Group, and was responsible for a large section of the Yugoslav-Hungarian border, deployed behind the Drava between Varaždin and Slatina.

The 4th Army was seriously weakened by fifth column activities within its major units and higher headquarters from 6 April, when the invasion commenced. Revolts of Croat soldiers broke out in all three divisions in the first few days, causing significant disruption to mobilisation and deployment. The formation and expansion of German bridgeheads across the Drava were facilitated by fifth column elements of the Ustaše and sympathetic units of the Civic and Peasant Guards of the Croatian Peasant Party. Elements of the 4th Army did put up scattered resistance to the Germans, but it 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. A senior staff officer at the headquarters of the 1st Army Group who sympathised with the Ustaše issued orders redirecting formations and units of the 4th Army away from the advancing Germans, and fifth column elements even arrested the headquarters staff of the 4th Army. Remnants of the 4th Army attempted to establish defensive positions in northeastern Bosnia, but were quickly brushed aside by the 14th Panzer Division as it drove towards Sarajevo. The Yugoslav High Command unconditionally surrendered on 18 April.

Composition
The 4th Army was commanded by Armiski đeneral Petar Nedeljković, and his chief of staff was Brigadni đeneral Anton Lokar. It was organised and mobilised on a geographic basis from the 4th Army District, which was divided into three divisional districts, each of which was subdivided into regimental regions. The 4th Army consisted of:  27th Infantry Division Savska 40th Infantry Division Slavonska 42nd Infantry Division Murska Infantry Detachment Ormozki (brigade-strength) 127th Infantry Regiment 81st Cavalry Regiment  Its support units included the motorised 1st Heavy Artillery Regiment, the 81st Army Artillery Regiment, the motorised 4th Anti-Aircraft Battalion, six border guard battalions and the motorised 4th Army Anti-Aircraft Company. The 4th Air Reconnaissance Group comprising eighteen Breguet 19s was attached from the Royal Yugoslav Air Force and was based at Velika Gorica just south of Zagreb. The troops of the 4th Army included a high percentage of Croats.

Deployment
The 4th Army was part of the 1st Army Group, which was responsible for the defence of northwestern Yugoslavia, with the 4th Army defending the western sector along the Hungarian border, and the 7th Army along the Reich and Italian borders. The 1st Cavalry Division was to be held as the 1st Army Group reserve around Zagreb. On the left of the 4th Army, the boundary with the 7th Army ran from Radgon on the Mura through Krapina and Karlovac to Otočac. On the right of the 4th Army was the 2nd Army of the 2nd Army Group, with the boundary running from just east of Slatina through Požega towards Banja Luka. The Yugoslav defence plan saw the 4th Army deployed in a cordon behind the Drava between Varaždin and Slatina. Of the formations of the 4th Army, the 40th Infantry Division Slavonska was partly mobilised, and the remaining two divisions had only commenced mobilisation. The planned deployment of the 4th Army from west to east was:  Infantry Detachment Ormozki just west of Varaždin, centred on Ivanec</li> 42nd Infantry Division Murska between Varaždin and Ludbreg, opposite the Hungarian city of Nagykanizsa</li> 27th Infantry Division Savska between Koprivnica and a point about 20 km east of Đurđevac, opposite the Hungarian village of Gyékényes</li> 40th Infantry Division Slavonska between a point about 10 km west of Virovitica and Slatina, opposite the Hungarian town of Barcs</li> </ul>

6–9 April
German Army headquarters wanted to capture the bridges over the Drava intact, and from 1 April had issued orders to the 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 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. In two regiments of the 42nd Infantry Division Murska, all but two battalions revolted and refused to deploy into their allocated positions. The 108th Infantry Regiment of the 40th Infantry Division Slavonska had mobilised in Bjelovar and on 7 April was marching towards Virovitica to take up positions. That night, Croat members of that regiment revolted, arresting 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.

10–11 April
Early on 10 April, Pukovnik Franjo Nikolić, the head of the operations staff with the headquarters of the 1st Army Group, left his post and visited the senior Ustaše leader Slavko Kvaternik in Zagreb. He then returned to 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; the 14th Panzer Division, supported by dive bombers, crossed the Drava and drove 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 the 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, reached Slatina by evening.

Later that day, as the situation was becoming increasingly desperate throughout the country, Simović, who was both the Prime Minister and Yugoslav Chief of the General Staff, broadcast the following message:

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, including 22 generals. Held up by freezing weather and snow storms, 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 and its commanding general. On 11 April, 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.

Fate
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. 14th Panzer Division first drove southwest to link up with Italian forces at Vrbovsko on 12 April, 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 8th and 14th Panzer Divisions entered Sarajevo. 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.