When the invasion commenced on 6 April, much of the division was deployed forward at Dravograd and Maribor, where, along with the border guard units along the frontier, it briefly held a defensive line.

The Kingdom of Serbs, Croats and Slovenes was created with the merger of Serbia, Montenegro and the South Slav-inhabited areas of Austria-Hungary on 1 December 1918, in the immediate aftermath of World War I.

[4] Consequently, at the time World War II broke out in September 1939, the VKJ had several serious weaknesses, which included reliance on draught animals for transport, and the large size of its formations.

[8][9] The weaknesses of the VKJ in strategy, structure, equipment, mobility and supply were exacerbated by serious ethnic disunity within Yugoslavia, resulting from two decades of Serb hegemony and the attendant lack of political legitimacy achieved by the central government.

In peacetime, the Dravska divisional district included:[12] The wartime organisation of the VKJ was laid down by regulations issued in 1936–37,[13] which set the strength of an infantry division at 26,000–27,000 men.

In what became the 38th ID sector, the Yugoslavs concentrated on preparing to block the passes through the Karawank and Savinja Alps, and built bunkers behind obstacles along the routes leading south from the border towards Dravograd and Maribor.

On 6 April, the elements of the division were located as follows:[28][29] The border between Germany and Yugoslavia was largely unsuitable for motorised operations due to the mountainous terrain.

[34] The LI Infantry Corps, commanded by General der Infanterie[e] Hans-Wolfgang Reinhard, was tasked with attacking towards Maribor then driving towards Zagreb.

The XXXXIX Mountain Corps, under General der Infanterie Ludwig Kübler, was to capture Dravograd then force a crossing on the Sava river at Zidani Most.

[37] By the end of the first day, LI Infantry Corps had occupied Gornja Radgona, Murska Sobota and Radenci, and had crossed the Drava near Sveti Duh.

[30] German Junkers Ju 87 Stuka dive bombers of Sturzkampfgeschwader 77, escorted by Messerschmitt Bf 109E fighters, attacked airfields in the rear area of the 7th Army later that day.

[39] By the close of the first day, the 7th Army was still largely mobilising and concentrating, and this, combined with delays caused by fifth column actions meant that nearly all the fighting was conducted by border troops.

German and Italian air attacks interfered with the deployment of troops and command was hampered by reliance on civilian telegraph and telephone services.

[41] In the early hours of 7 April, three Blenheims of the Yugoslav 8th Bomber Regiment took off from Rovine to bomb the railway junction at Feldbach, but became disoriented in bad weather.

Only one aircraft found a target, bombing a bridge and road near Steyr before continuing on to Wiener Neustadt where it was hit by anti-aircraft fire and made an emergency landing.

The German thrusts towards Maribor broke through the Yugoslav defensive line Pesnica–Lenart–Sveta Trojica v Slovenskih Goricah–Kapelski Vrh, but those advancing towards Dravograd were held up by the 6th Border Regiment and a battalion of the 38th ID.

[45] Disregarding orders from above, Palten exploited their withdrawal by leading his kampfgruppe south towards the town, and crossing the Pesnica river in inflatable boats, leaving his unit vehicles behind.

The 38th ID continued to withdraw south from Ptuj through Krapina towards Zagreb, while the Mountain Detachment Triglavski on its left flank fell back to the southern bank of the Krka river.

Rupnik and the head of the operations staff of the headquarters of the 1st Army Group, Pukovnik[g] Franjo Nikolić, who were both Slovenes, hid the orders from Petrović and did not carry them out.

[41][51] On the evening of 9 April, Weichs ordered the XXXXVI Motorised Corps of General der Panzertruppe[h] Heinrich von Vietinghoff to break out of its bridgeheads in the 4th Army's sector the following day.

[53] Before it arrived, the Ustaše, supported by German agents, had proclaimed the creation of the puppet Independent State of Croatia (Croatian: Nezavisna Država Hrvatska, NDH).

[55] In the 7th Army sector, about 09:45, the LI Infantry Corps began crossing the Drava, but construction of a bridge near Maribor was suspended because the river was in flood.

[52] This crossing point was a partially destroyed bridge, guarded by a single platoon of the 1st Bicycle Battalion of Detachment Ormozki, the formation on the immediate right flank of the 38th ID.

[57] 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.

[37] On 10 April, as the situation was becoming increasingly desperate throughout the country, Simović, who was both the Prime Minister and Chief of the General Staff, broadcast the following message:[58] All troops must engage the enemy wherever encountered and with every means at their disposal.

[61] Chaos ensued throughout the 7th Army, whose Croat and Slovene soldiers could hear fifth column radio broadcasts telling them of their pending encirclement by the Germans and encouraging them to return to their homes and not fight against the invaders.

[63] Held up by freezing weather and snow storms, LI Infantry Corps was approaching Zagreb from the north,[55] and broke through a hastily established defensive line south of Ptuj between Pregrada and Krapina.

[55] When the Italian 14th Infantry Division Isonzo entered Ljubljana, a delegate of the NszS greeted its commander, Generale di Divisione[i] Federico Romero, and symbolically handed him the keys to the city.

The meeting was very formal and cold, as Lanz had already received orders regarding the break-up of the Drava Banovina into Italian and German-controlled territories, and the council and its goal of an independent Slovenia were superfluous from a German perspective.

[66] Remnants of the 4th Army conducted a fighting withdrawal through Bosnia towards Sarajevo over the following days, pursued by the 14th Panzer Division and elements of LI Infantry Corps but a ceasefire was declared at noon on 15 April.