Invasion of Yugoslavia

The invasion of Yugoslavia, also known as the April War or Operation 25, was a German-led attack on the Kingdom of Yugoslavia by the Axis powers which began on 6 April 1941 during World War II. The order for the invasion was put forward in "Führer Directive No. 25", which Adolf Hitler issued on 27 March 1941, following a Yugoslav coup d'état that overthrew the pro-Axis government.

The invasion commenced with an overwhelming air attack on Belgrade and facilities of the Royal Yugoslav Air Force (VVKJ) by the Luftwaffe (German Air Force) and attacks by German land forces from southwestern Bulgaria. These attacks were followed by German thrusts from Romania, Hungary and the Ostmark (modern-day Austria, then part of Germany). Italian forces were limited to air and artillery attacks until 11 April, when the Italian Army attacked towards Ljubljana (in modern-day Slovenia) and through Istria and Lika and down the Dalmatian coast.

The invasion ended when an armistice was signed on 17 April 1941, based on the unconditional surrender of the Yugoslav army, which came into effect at noon on 18 April. The Kingdom of Yugoslavia was then occupied and partitioned by the Axis powers. Most of Serbia and the Banat became a German zone of occupation while other areas of Yugoslavia were annexed by neighboring Axis countries, Germany, Hungary, Italy, Albania and Bulgaria. Croatia became the Independent State of Croatia (NDH), an Axis puppet state created during the invasion comprising the Srem, Bosnia and Herzegovina as well as the Croatian lands.

Background

See also: Greco-Italian War and Yugoslav coup d'état

In October 1940, Fascist Italy attacked the Kingdom of Greece but was pushed back into Italian-occupied Albania. To help his ally Benito Mussolini, German leader Adolf Hitler decided to support Italy. He wanted to protect important oil supplies from Romania and keep the Axis powers strong.

Later, Hungary, Romania, and Bulgaria joined the Axis by signing the Tripartite Pact. Hitler also pushed Yugoslavia to join. The regent, Prince Paul, agreed on 25 March 1941, but this made many people unhappy, especially in the military. On 27 March 1941, military officers staged a coup, removed Prince Paul, and declared young King Peter II ready to rule.

Preparation

Upon hearing news of a change in leadership in Yugoslavia, Adolf Hitler called his military advisers to Berlin on 27 March 1941. On that same day, he issued Führer Directive No. 25, which called for Yugoslavia to be treated as a hostile state. Hitler felt very angry about the change in leadership and decided to plan an attack on Yugoslavia.

Hungary had joined an agreement with Germany on 20 November 1940. On 12 December, it also made a treaty with Yugoslavia for peace and friendship. However, after Germany's plans for attack were shared on 27 March 1941, Hungary's leaders were divided about whether to join in the attack. Some, like Regent Miklós Horthy, wanted to help Germany, while the Prime Minister, Pál Teleki, wanted to stay neutral because of the peace treaty.

On 1 April, Yugoslavia reorganised its military commands in preparation for possible defense. On 2 April, Germany began preparing to leave Yugoslavia, signaling that an invasion was coming. On 3 April, Hitler issued more detailed plans for the attack, promising Hungary some land gains if they joined. Later, Hungary agreed to the invasion after a new state was proclaimed in Croatia.

Opposing forces

Axis order of battle

The invasion was led by Germany, with support from Italy and Hungary. Germany used parts of its 2nd Army, including panzer divisions and many aircraft. Italy sent two armies with around 300,000 troops, and Hungary also joined the attack. The forces were well-equipped and ready to move quickly.

Germany attacked from bases in Hungary, Romania, and Bulgaria. In Romania, German troops arrived under the idea of training Romania’s army but were really there to protect important oil supplies and prepare for attacks on the Soviet Union. In Bulgaria, German forces arrived to defend Romania’s oil fields and to support Italy in attacking Greece. Hungarian forces agreed to let German troops pass through and later joined the fighting against Yugoslavia.

Royal Yugoslav armed forces

Yugoslavia’s defenses were not fully ready when the attack began. The army had many divisions but relied on older equipment and animals for transport. They had few modern tanks and faced problems with incomplete mobilization and supplies. The air force had around 400 planes, but many were not the most modern types. The navy was small, with a few destroyers and submarines.

Yugoslavia’s army was split into three groups, with the strongest facing Romania, Bulgaria, and Albania. Another group defended areas near the Iron Gates and Drava River, and the last group was in Croatia and Slovenia. However, the army was not fully prepared, and some troops were not even in their positions when the attack started. There were also problems within the army, as not all groups were willing to fight together, which made the defense weaker.

Operations

Professor Jozo Tomasevich and others divide the invasion and resultant fighting into two phases. The first phase includes the Luftwaffe's air assault on Belgrade and airfields of the Royal Yugoslav Air Force on April 6, and an initial thrust of the German XL Panzer Corps from Bulgaria towards Skopje. This was followed by the assault of the German XIV Panzer Corps from Bulgaria towards Niš on April 8. On April 10, four more thrusts struck the Yugoslav Army; the XLI Panzer Corps from Romania towards Belgrade, the XLVI Panzer Corps from Hungary across the Drava, the LI Infantry Corps from Austria towards Zagreb, and the XLIX Mountain Corps from Austria towards Celje. By the end of that day, the Yugoslav Army was disintegrating, and was in retreat or surrendering across the country, except for the forces on the Albanian frontier. Italy and Hungary joined the ground offensive on April 11.

The Luftwaffe and Regia Aeronautica had superior numbers, tactics, and combat experience. Despite having modern aircraft, the Royal Yugoslav Air Force struggled to match this strength. The VVKJ conducted bombing and strafing missions against Axis troops and provided air support to the hard-pressed Yugoslav Army. However, after 11 days of intense fighting and losses from air combat, ground attacks, and overwhelmed airfields, the VVKJ almost ceased to exist. Limited aircraft production during the invasion supplied a few additional planes.

Bombing of Belgrade

Main article: Operation Retribution (1941)

On April 6, the Luftwaffe launched a massive bombing raid on Belgrade, known as "Operation Retribution." Around 300 aircraft, including Junkers Ju 87 Stukas, attacked the city in three waves. The bombing targeted government buildings and communication centers, severely disrupting the Yugoslav high command's ability to coordinate defenses. The VVKJ fighters, including Messerschmitt Bf 109s, Hurricanes, and Rogozarski IK-3s, engaged the bombers but suffered significant losses. The bombing effectively crippled Belgrade's defenses and infrastructure.

Ground operations

The British, Greek, and Yugoslav high commands intended to use Niš as a key point to wear down German forces. However, when German forces broke through this sector, the Yugoslav Supreme Command committed strategic reserves, including the 2nd Cavalry Division, which faced harassment from the Luftwaffe during transit. The German 14th Motorised Corps moved north towards Belgrade, while the 46th Panzer Corps advanced from Austria, and the 41st Panzer Corps threatened from Romania and Hungary. By April 11, German armored columns had crisscrossed Yugoslavia, leaving only a large nucleus of the Yugoslav Army around Belgrade still resisting. On April 12, Belgrade surrendered after a German officer bluffing about his forces' size convinced the city’s mayor.

Italian offensive

In the opening days of the invasion, Italian forces on the Slovene border carried out minor actions, capturing several positions. On April 11, the 2nd Army launched its offensive, capturing Ljubljana, Sušak, and Kraljevica. The 133rd Armoured Division Littorio and the 52nd Infantry Division "Torino" took Senj, and Italian naval forces occupied several Dalmatian islands. Split and Šibenik were taken on April 15 and 16, respectively, and on April 17 the Motorized Corps took Dubrovnik.

Hungarian offensive

Main article: Hungarian occupation of Yugoslav territories

On April 12, the Hungarian Third Army crossed the border with cavalry, motorized, and infantry brigades. Facing little resistance, Hungarian forces advanced into southern Baranja, Bačka, and the Vojvodina region, occupying territories that were part of Hungary before the Treaty of Trianon.

Yugoslav Albanian offensive

In accordance with the Yugoslav Army's war plan, R-41, an offensive strategy was formulated to launch attacks against Italian forces in Albania while retreating on all other fronts. The 3rd Yugoslav Army, in cooperation with the Greek Army, was to secure space for the withdrawal of the main Yugoslav Army to the south via Albanian territory to reach Greece and Allied forces. The offensive began on April 7, with units advancing towards Shkodër and other areas, but progress was limited due to German advances and Italian code-breaking efforts that disrupted Yugoslav communications.

Naval operations

When Germany and Italy attacked Yugoslavia on April 6, 1941, the Yugoslav Royal Navy had limited effective units, including three destroyers, two submarines, and 10 motor torpedo boats. One destroyer, Ljubljana, was in dry-dock and used for defense. Naval forces attempted attacks on Italian positions and convoys but faced significant challenges. The river monitors Drava, Sava, Morava, and Vardar patrolled northern rivers but were attacked by German dive-bombers. Drava was damaged and later scuttled, while the others were scuttled by their crews as German and Hungarian forces occupied their bases.

Romanian involvement

While Romania did not take part in the actual invasion of Yugoslavia, it provided artillery support for German forces invading from its territory. Romanian artillery opened fire against Yugoslav barges on the Danube on April 6. Romanian and German units exchanged fire with Yugoslav forces between April 6 and 11. For its contribution, Romania was rewarded with six ex-Yugoslav aircraft captured by the Germans, though these were inoperative and largely unusable.

Losses

The German forces faced surprisingly few losses during their attack on Yugoslavia. In just twelve days of fighting, around 558 German soldiers were affected — some were killed, others were wounded, and a few went missing. The German air force lost about 60 airplanes.

Italy and Hungary also fought in the invasion and faced more challenges. The Italian army lost around 800 soldiers, while the Hungarian army lost about 350. Many airplanes from different countries were shot down or damaged during the battles.

Yugoslav forces lost a large number of soldiers and many airplanes. Over 250,000 Yugoslav soldiers were captured, though some escaped to continue fighting with Allied forces in other countries.

Armistice and surrender

The Axis powers quickly won the battle. By April 14, Yugoslav leaders decided to ask for peace and sent messages to the Germans. They were told that only giving up completely would be accepted. On April 17, after just eleven days of fighting, Yugoslav leaders signed an agreement to stop all fighting. This agreement started on April 18 at noon.

Some people think the Yugoslav army was not well trained or equipped, which helped the Axis win. Others believe that problems within Yugoslavia, like lack of good leaders and old ways of fighting, were bigger reasons for the quick defeat. Different groups had various ideas about why the army lost so fast.

Aftermath

Main article: World War II in Yugoslavia

After the surrender in 1941, Yugoslavia was divided among Germany, Hungary, Italy, and Bulgaria. Germany took control of most of Serbia, while Croatia was under joint control of Germany and Italy.

Resistance began quickly under Royal Yugoslav Army Colonel Draža Mihailović in the mountains of Serbia and Eastern Bosnia. He was made a general by King Peter II and his government-in-exile in Britain. Soon after, the Yugoslav Partisans led by Josip Tito also started fighting the Axis powers. Over time, the Partisans became the main resistance force, supported by the Allies.