'First Enemy Offensive' was Yugoslav designation for the German and Četnik 'Uzice' offensive against the partisan forces of Josip Broz Tito in the western part of German-occupied Serbia (27 September/15 October 1941).

The 'First Enemy Offensive' was the initial major military confrontation on the Yugoslav front in World War II after the fall of the country in 'Unternehmen 25', and took the form of an offensive by German and allied troops against the so-called Uzice Republic, which was the first of a growing number of self-contained liberated territories created by the partisan resistance forces. For the initial defence of the territory the partisans were aided by Pukovnik Dragoljub 'Draza' Mihailović's Četnik units, and it was during this offensive that tenuous collaboration between the communist partisan and royalist Četnik movements first broke down and then turned into open hostility.

The first Yugoslav partisan unit had been established in Brezovica forest, near Sisak in German-occupied Croatia on 22 June 1941. Various military formations more or less linked to the general liberation movement were involved in armed confrontations with Axis forces which erupted in several parts of German-occupied Yugoslavia in the following weeks, and the Communist Party of Yugoslavia formally decided to launch an armed uprising on 4 July. On 7 July, while the Četnik forces were still inactive, Tito and the partisans began a large uprising in the region between Sabac and Usice, in the Krupanj area of north-western Serbia. The uprising was successful and secured a defensible, self-sustained and independent region, the so-called Usice Republic and thus the first of many 'free territories' established by the partisans during the course of the war.

Almost immediately the Germans made a concerted effort to find out whether or not the Četniks supported the uprising, as they felt that only with nationalist support could it acquire a mass character. On 14 August the headquarters of General Heinrich Danckelmann’s Befehlshaber 'Serbien' command reported to the Oberkommando der Wehrmacht that the partisan forces at this stage were not supported by the Četnik nationalists. Despite this, the German military forces in the region were deemed insufficient to quell the uprising, which by 27 August had become more threatening and was spreading. Because of this, and since no reinforcements could be expected, the German authorities decided to rely on enlarging their Serb auxiliary forces to provide greater strength and a local force with which to defeat the communist partisans.

By September 1941, after seeing the considerable success of the uprising, and observing its wide, and growing, support among the populace, the Četniks realised that if they did not join the communists they would probably lose their standing as the leaders of Serb resistance.

On 12 September German intelligence noted that Četnik units were on the move to support the partisans. In mid-September Tito and the partisan general staff moved from Belgrade to the Usice Republic, where the partisans had by now formed 25 new partisan detachments. On 19 September Tito and Mihailović met to negotiate an alliance between the partisans and the Četniks, but failed to reach an agreement: while Tito wished to launch a joint full-scale offensive, Mihailović considered a general uprising of this nature to be premature and dangerous as, he believed, it would inevitably trigger major Axis reprisals. Thus Četnik support for the rising was only partial: of some 5,000 to 10,000 men currently available to them, the Četniks fielded about 3,000 in the area, and of these a sizeable proportion did not fight.

Meanwhile, on 16 September Generalfeldmarschall Wilhelm Keitel, head of the Oberkommando der Wehrmacht, issued an order (application to all parts of German-occupied Europe) that 50 hostages were to be killed for every German soldier who was wounded, and 100 for every German soldier who was killed. General Franz Böhme, the German military commander in Serbia, ordered that Keitel’s directive be carried out ruthlessly. Böhme made it clear from the beginning that he intended if necessary to wage war against the whole Serb population by considering all civilians as enemies. He was also instructed to apply the order concerning the taking of hostages not just to attacks on German military personnel, but also to those on ethnic Germans, Bulgarian military personnel, individuals in the service of the occupation authority, and eventually to members of the Serb administration. Each act of insurgency was to be considered of communist origin.

The German military declared Serbia a war zone and began to burn villages. When 10 German soldiers were killed in a joint partisan and Četnik attack on Kraljevo, the Germans shot 1,700 hostages on 20 October. Several thousand more hostages were executed during the following weeks in reprisal for insurgent attacks.

In an effort to clear the Usice Republic of partisans, the Germans employed Generalleutnant Dr Walter Hinghofer’s 342^nd Division and Generalleutnant Friedrich Zickwolff’s 113^th Division as well as elements of Generalmajor Heinrich Borowski’s 704^th Division, Generalleutnant Friedrich Stahl’s 714^th Division, Generalmajor Paul Hoffmann’s 717^th Division and Generalleutnant Johann Fortner’s 718^th Division. The German formations were supplemented by Dimitrije Ljotić's Serb Volunteer Corps and Kosta Pećanac’s forces as well as Ustase and Croat Home Army elements, and by the Croats' concurrent 'Visegrad' undertaking.

As these forces entered the territory held by the partisans, they faced significant resistance, especially on Rudnik mountain and in Kraljevo. As retribution for a lost man, the Germans are claimed to have executed 7,000 people in Kragujevac on 21/23 September.

The offensive began officially on 29 September when the 342^nd Division attacked partisans along the road linking Sabac and Loznica. As the weight of the German offensive began to become clear at the beginning of October, Tito tried to negotiate help from Mihailović and his Četniks. At this time several small Serb towns were in the hands of partisan or Četnik groups. While distrustful of each other, the partisans and Četniks started to take joint action in matter such as the sieges of larger towns. The partisan and Četnik headquarters were currently located at Usice and Pozega, some 9 miles (15 km) apart. During October, though, all hope of continued co-operation failed as sporadic bickering and outright violation of agreements became common. During these weeks it also became obvious that while the partisans were adamant on the need to continue the fight, the Četniks were considering ways in which they could abandon the fight against the Germans and direct their energies against the partisans. Over a period of several weeks the two parties became increasingly more polarised, and the Četnik detachments led by Vlada Zećević and Ratko Martinović switched their allegiance to the partisans during this time.

Tito and Mihailović met again on 27 October in Brajići in the Ravna mountain region in a last attempt to achieve an understanding, but could agree only on secondary matters. Indeed, the Četniks had already despatched Pukovnik Branislav Pantić and Kapetan Nenad Mitrović, two of Mihailović's aides, to Belgrade for a 28 October meeting with an officer of German military intelligence, Hauptmann Josef Matl. The two Četnik officers informed Matl that they had been empowered by Mihailović to establish contact with the collaborationist prime minister, Milan Nedić, and the appropriate German commanders to inform them that the Mihailović was willing to align the Četniks with the Axis forces in the fight against communism. The two Četnik officers also gave the Germans their leader’s guarantee for the clearance of 'communist bands' from Serb territory and asked for aid in the form of about 5,000 rifles and 350 machine guns, the latter including 20 heavy machine guns.

After more than a month of disagreements and minor collisions, events peaked on 1 November in a major Četnik attack in and around the town of Usice, where the partisans had their headquarters. Apparently underestimating partisan strength, the Četnik forces were quickly beaten back.

At this point the British liaison officer in Yugoslavia advised the Middle East Command in Cairo to stop supplying the Četniks so that British arms would not be used in a civil war. The Četniks, who had already received by parachute one shipment of weapons, now waited in vain for a second one: the British later resumed aid to the Četniks.

Both Tito and Mihailović were still willing to establish an armistice, however, although both were pressed by some of their officers to attack the other as soon as possible. Thus there emerged a succession of ceasefires and ultimata which served as punctuation marks in an escalating series of reciprocal reprisals that degraded both parties' local credibility and indeed alienated the civilian population.

Mihailović soon saw that his forces could not protect Serb civilians against German reprisals and, in the face of indiscipline and a lack of ammunition, discovered that his forces were being decimated by the conflict with both Germans and partisans. A meeting was arranged between Matl and Pantić, who agreed the utility of a direct meeting between Mihailović and German military intelligence representatives. This took place in Divci on 11 November, but the exact circumstances of the meeting remain controversial. There are indications that Mihailović offered to cease Četnik activities in German-controlled towns and along the major German lines of communication, but ultimately no agreement was reached in this meeting as Germany demanded the complete surrender of the Četniks After the negotiations the Germans sought without success to seize Mihailović.

Meanwhile German and allied forces advanced from the north and east toward Usice, and by the second half of November the partisan forces were in full retreat.

On 25 November the last stage of the German offensive against both resistance groups began. Tito and Mihailović had a final telephone conversation: Tito announced that he would defend his positions, while Mihailović said that he would disperse his forces. On 29 November the partisans and their headquarters left Usice. On 10 December, a bounty was put on the head of Mihailović, while he himself narrowly escaped capture. Mihailović decided on the temporary disbandment of most of his forces, and with his small staff fell back into the Ravna mountain area, where his cadre remained under German attack throughout December.

Both Tito and Mihailović had suffered major setbacks. Tito had been surprised by the scale of the uprising, and had found himself managing inexperienced peasant fighters, who were reluctant to move away from their towns, or to accept authority and indoctrination. Mihailović had also been unable to impose discipline on his officers.

The partisans left Usice for Sandzak in Italian-occupied territory. Some detachments failed to retreat on time and were dispersed or destroyed. After the main partisan forces had left for Sandzak, only parts of five partisan detachments remained in Serbia.