'Panzerfaust' was the German seizure, otherwise known as 'Eisenfaust', of Burberg Castle in Budapest, the Hungarian capital, at the time that the Hungarian regent, Vezérfökapitány Miklós Horthy de Nagybánya, broadcast to the Hungarian people that he had secured an armistice with the Soviets (15/16 October 1944).

When Adolf Hitler received word that the Hungarian regent, Horthy, was using his son to undertake secret negotiations to surrender Hungary to the advancing Soviet forces, he despatched to Hungary SS-Obersturmbannführer Otto Skorzeny, Germany’s best known exponent of special forces operations, and Adrian Graf von Fölkersam, formerly an officer on a 'Brandenburger' special forces unit and currently on the strength of the SS-Jagdverband 'Ost'. Hitler feared that a Hungarian surrender would expose Germany’s southern flank, where Romania had recently defected and joined the Soviets, in the process cutting off some 1 million German troops still fighting the Soviet advance in the Balkan peninsula, and also remove from any possibility of German exploitation Hungary’s manpower, industry and natural resources. The 'Panzerfaust' operation followed the 'Margarethe' undertaking of March 1944, when German forces had occupied Hungary and which Hitler had hoped would secure Hungary’s continued adherence to the Axis.

Skorzeny’s remit was to bring about the removal of Horthy from power. Horthy’s son, Miklós, was informed by the German security service, via intermediaries, that envoys of Josip Broz Tito of Yugoslavia wanted to meet with him. The son did not arrive at the first planned meeting after he saw suspicious individuals near the proposed meeting place, and a second meeting was arranged for a time early on 15 October at the offices of Felix Bornemisza, the director of the Hungarian ports on the Danube river. The younger Horthy hoped that the Yugoslav representatives might have important news, but as he entered the building he was attacked and seized by Skorzeny and men of his 600^th SS Fallschirmjägerbataillon, who then rolled him into a carpet, drove him to the nearest airfield and flew him to Vienna, from which he was transported to the concentration camp at Mauthausen.

At this time, through a trusted intermediary, Altábornagy Béla Dálnoki-Miklós, commander of the Hungarian 1^st Army, Horthy was in contact with the Soviet forces in the eastern part of Hungary, and was attempting to negotiate an end to Hungary’s involvement in the war by seeking to surrender to the Soviets while nonetheless preserving the government’s autonomy. Although Horthy was an intractable anti-communist, his dealings with the Nazis had led him to conclude that the Soviets represented a lesser evil. In an effort to bring Hungary into their fold, the Soviets gladly promised that Hungary would remain autonomous and sovereign.

Horthy’s administration was based on Castle Hill in the centre of Budapest, which was an old but well-guarded fortress. Horthy blamed the German government for 'forcing' Hungary into World War II, and during a meeting of the Crown Council declared that it was clear that Germany was losing the war, that all governments responsible for the destiny of their countries had to draw the appropriate conclusions from this fact, and that he had therefore decided to safeguard Hungary’s honour, even against a former ally (though this ally, instead of supplying the promised military help, in fact intended to rob the Hungarian nation of its freedom and independence), and therefore informed a German representative that Hungary was about to conclude a military armistice with the USSR and to cease all hostilities against it.

At 14.00 on 15 October, Horthy announced in a national radio broadcast that Hungary had signed an armistice with the Soviets. However, the Germans had been aware of Horthy’s secret negotiations and already set in motion plans to replace his government with another which was loyal to the German alliance, effectively occupying Hungary. With Nazi help, supporters of the rival Arrow Cross Party – Hungarian Movement seized the radio station shortly after the end of Horthy’s broadcast. A party member wrote a counter-proclamation which was broadcast over the name of the Hungarian army’s chief-of-staff, Vezérezredes János Vörös. The commander and senior officers of the two Hungarian army units remaining in Budapest were arrested or 'disappeared', and their units declared their adherence to the new regime.

Many Hungarian formations and units were already under German control, and it is unclear whether or not orders to resist, if they were in fact issued, ever reached most of the men, most of whom had been bombarded with propaganda about the harsh, punitive treatment of their prisoners by the Soviets.

Skorzeny then led a force of German troops and four Tiger II heavy tanks to the Vienna Gates of the Burberg. Appreciating that there was no way to fight off the German tanks and infantry, Horthy ordered that there should be no resistance. One Hungarian unit did not receive the order, however, and fought the Germans for about 30 minutes. The Germans quickly and with minimal bloodshed captured the Burberg. Only seven men were killed and 26 wounded.

Horthy was taken into custody by SS-Brigadeführer Edmund Veesenmayer (later the Reich Plenipotentiary in Hungary) and his staff later on 15 October. Kept overnight in the Waffen-SS offices, Horthy was then allowed to return to the palace to collect his personal belongings. While there, he was confronted with a demand to sign a typewritten statement handed to him by the prime minister, Vezérezredes Vitéz Lófő Géza Lakatos de Csíkszentsimon. The statement announced that Horthy was renouncing the armistice and abdicating in favour of Ferenc Szálasi, the leader of the Arrow Cross Party – Hungarian Movement. Surprised that his erstwhile loyal friend would encourage him to sign the document, Horthy was told by Lakatos that his son’s life was at stake, and when Horthy asked Veesenmayer if this was true, the latter confirmed the threat. Horthy rightly surmised that this was an attempt to legitimise was was in fact a coup d'état, but nonetheless appended his signature. Lakatos was also forced to resign later in the same day.

Hungary continued to fight, albeit largely unwillingly, alongside Germany until April 1945. The German reaction to Hungary’s attempt to reach a separate accord with the USSR had totally alienated an already unenthusiastic nation, and the result was that Dálnoki-Miklós, commander of the Hungarian 1^st Army, defected to the Soviets after telling the Hungarians to treat the Germans as the enemy, but Altábornagy Lajos Dálnoki-Veres, commander of the Hungarian 2^nd Army, was arrested at the orders of Generaloberst Johannes Friessner, commander of Heeresgruppe 'Süd', before he could emulate this act.

Despite Veesenmayer’s promise to obtain the release of Horthy’s son from the concentration camp in which he was being held, the younger Horthy remained a prisoner until the end of World War II on 8 May 1945. Horthy himself was transported to the Schloss Hirschberg near Weilheim in Germany, and held in captivity by a guard force of 100 Waffen-SS soldiers. On 1 May 1945, Lieutenant General Alexander McC. Patch, the commander of the US 7^th Army, visited Horthy, who was now considered to be a prisoner of war until released seven months later on 17 December 1945.