The 'Trsćanska Operacija' was the Yugoslav operation by the forces of Marshal Josip Broz Tito to liberate Trst (Trieste) and the region round it from occupation by the Axis forces (29 April/1 May 1945).

The operation became a joint Allied victory for the Yugoslav forces and Lieutenant General Sir Bernard Freyberg’s New Zealand 2^nd Division, and led to the joint occupation of Trieste, but relations between the two parties soon deteriorated and led to a nine-year dispute over the territory of Trieste. The operation is also considered the last battle in which a considerable force Četniks was involved, as 13,000 of the irregular troops surrendered to the New Zealand forces as the battle progressed.

The Yugoslav forces had achieved a breakthrough after a series of hard-fought encounters along the Syrmian front late in 1944 and early in 1945. Present at the pivotal Battle of Knin, the Yugoslav 4^th Army then spent most of the spring and early summer of 1945 in an advance to the north through Dalmatia with the object of taking Trieste and the Istrian peninsula without any support by the Western Allies, thereby justifying a claim to this Italian port and region.

The 4^th Army was led by General dupovnik Petar Drapsin, who had previously led the VIII Corps.

On the north-eastern sector of the Italian front, the Western Allied forces were advancing toward Trieste after breaching the 'Gotische-Linie' defences early in March 1945. Freyberg’s New Zealand 2^nd Division, having captured Faenza on 14 December 1944, was reorganised on the southern bank of the Senio river on 8 April 1945, and paused here in preparation for what was to become the final Allied offensive in Italy. After a brief rest, the division pressed forward at speed, crossing the Santerno, Gaiana, Idice and the Po rivers. The division took Padua on 28 April, crossed the Isonzo river on 1 May and reached Trieste on the following day. The division had covered 140 miles (220 km) in less than one week.

The civil authorities in Trieste, formally part of the Italian Social Republic although actually under German control through the Befehlshaber Operationszone Adriatisches Küstenland (commander of the Adriatic coastal zone of operations) consisted of a prefect and a mayor, who were Bruno Coceani and Cesare Pagnini respectively. Italian resistance forces were active within the city through the local national liberation committee headed by the socialist Carlo Schiffrer, christian democrat Edoardo Marzari, action party member Ercole Miani and liberal party member Antonio Selem. The representatives of the Italian communist party had withdrawn from the local committee of national liberation in the summer of 1944 in the aftermath of disagreements about the level of co-operation with the Yugoslav partisans and national army: the communists favoured an alliance, but the other parties feared that the Yugoslavs intended to annex Trieste to Yugoslavia.

Early in April 1945, Coceani had proposed to Pagnini and, through the latter, to Schiffrer that all the Italian forces be united in an anti-Yugoslav liaison, in an attempt to try to stem the advance of Josip Broz Tito’s forces and thus make it possible for the Western Allies to reach and occupy Trieste first. On 4 April, Coceani asked Benito Mussolini, titular head of the Italian Social Republic, for support in the defence of Trieste and, for the exactly the same purpose, also sent emissaries to Rome in order to contact the royalist government in an attempt to obtain help for the defence of the eastern border. Ammiraglio di Squadra Raffaele Conte de Courten, the chief-of-staff of the Italian co-belligerent navy, answered positively, and a landing by forces of the Regia Marina, with the support of the X Flottiglia MAS and of other troops, had been planned, with or without Allied intervention. The plan failed, however, as a result of British opposition. On 10 April Pagnini held an organisational meeting of 500 Italians with the aim of uniting all Italian forces, avoiding attacks on the Germans, who as long as they defended the city against the Yugoslavs were to be considered allies, and transferring all powers to the committee of national liberation as soon as the Germans departed. It was decided that the 1,800 men of the Guardia Civica (civic guard), which had been raised in 1944 by Coceani as Trieste’s municipal police, would also come under command of the committee of national liberation.

On 28 April Bruno Sambo, head of the local republican fascist party, handed over the fascist party’s weapons to Coceani’s public health committee, and agreed to replace the party insignia with tri-colour ribbons. During the evening of the same day, some Italian police units came out onto the streets with the tri-colour ribbons, but were quickly disarmed by the Germans. In the meantime, however, after lengthy discussions, the local committee of national liberation decided to reject Coceani’s proposals to join forces against the Yugoslavs, and decided to act against the Germans. On the night of 29/30 April, all German troops in Trieste were ordered by Odilo Globočnik to withdraw toward Tolmezzo, a fact of which Ercole Miani, the local head of the committee of national liberation, was informed by Coceani, and on the next morning the committee of national liberation proclaimed a general insurrection against the Germans. Carabinieri and Guardia di Finanza troops defected to the resistance, Coceani resigned and the committee of national liberation assumed all powers after clashes against the remaining German and Fascist troops.

The Yugoslav operation began with the advance of the main strength of Dapčević's 4^th Army toward Trieste. The army’s two operational groups advanced along the axes from Ilirska Bistrica to Divača and Trieste, and from Lovran through Istria to Trieste, while the IX Corps advanced over Kras toward Trieste, Monfalcone and Gorica. By 30 April units of the 4^th Army had surrounded Trieste and, with concentric attacks and the aid of partisan forces in the city, took Trieste on 1 May after heavy fighting.

In street fighting against units of the German defence, elements of the 20^th Division captured the university, military hospital and railway station by direct assault. The 11^th Brigade of the 26^th 'Dalmatia' Division reached coast at the San Marco docks, while the 3^rd Brigade of the 43^rd Division cleared the Milje peninsula and captured Zavlju. The German stronghold at Opičine was captured on 3 May, and during the first days of May the Yugoslav forces liberated the entire Slovenian littoral, Beneska Slovenia and Istria.

General Ludwig Kübler’s LXXXXVII Corps capitulated on 7 May, and with the advance of the 4^th Army’s Motorised Detachment toward Koruska and of the 29^th Division and VII Corps toward Ljubljana, the 'Trsćanska operacija' was complete after more than 5,200 Germans had been taken prisoner and substantial numbers either killed or wounded.

The Axis troops in the Trieste area were the remnants of various formations and part of the Küstenverteidigungsabschnitt 'Triest' (Trieste Coast Defence Sector) local defence force from the Milje (Muđa, Mugga) peninsula to the Soca river. This defensive force had three coastal artillery and two anti-aircraft artillery battalions, five infantry battalions and one mixed battalion, and also numerous naval and army installations. In addition, Generalleutnant Wilhelm von Hösslin’s 188^th Gebirgsdivision and Oberst Karl Falkner’s 237^th Division of the LXXXXVII Corps were present in Istria, there were several police battalions of the Italian Fascist militia, around Gorica there was the 10^th SS Polizeiregiment, and David Damjanović's Srpski Dobrovoljački Korpus (Serb Volunteer Corps) and Vojvoda Momčilo Đujić's Četnik 'Dinara' Division, initially allocated to the task of railway security in Istria, were used in combat around Iliriska Bistrica and sent to Soca.

By 30 April, the Yugoslav forces had surrounded Trieste, and during the morning of 1 May started to advance with the aid of fighters who had infiltrated the city before the arrival of the Yugoslav main forces. By 30 April elements of the Yugoslav forces had taken many strategic locations from Globočnik’s forces, these including the university, courthouse and military hospital. On the morning of 1 May, parts of the Yugoslavs' eastern force broke through at Ricmanje and Botač and entered the city. According to Yugoslav reports, Italian and German resistance had been overcome in most places except a few isolated pockets of Germans, especially in the area of Opčine and the harbour. By the evening of 1 May, Yugoslav forces had taken the Elba battery factory and Sabo park, where they were joined by about 50 armed anti-Fascist citizens of Trieste, There the 4^th Brigade of the 9^th 'Dalmatia' Division met and attacked a force of about 1,000 German and Četnik soldiers. On the morning of 2 May this culminated in a two-hour firefight that was followed by the surrender of the German and Četnik troops.

By the end of 2 May, with the arrival of the New Zealand 2^nd Division, most of the 13,000 Četnik irregulars assisting the German defenders had surrendered. Some fighting continued into the next day, and the remaining German pockets on the northern side of the city, of which the largest was the Opčine pocket, had surrendered by the end of 3 May.

Trieste was occupied jointly by the New Zealanders and Yugoslavs until June 1945, when the area came under rule of a United Nations-mandated military provisional government as an element of the peace treaty with Italy. Trieste and the Istrian peninsula were to remain a de facto free state until the area was partitioned between its two neighbours in October 1954. This was later reaffirmed in the Treaty of Osimo, where it was split de jure between Italy and Yugoslavia.