The Vardar offensive () was a World War I military operation, fought between 15 and 29 September 1918. The operation took place during the final stage of the Balkan Front. On 15 September, a combined force of Serbian, French, and Greek troops attacked the Bulgarian-held trenches in Dobro Pole ("Good Field"), at the time part of the Bulgarian-occupied Kingdom of Serbia and the Kingdom of Greece (present-day North Macedonia and Greece). The assault and the preceding artillery preparation had devastating effects on Bulgarian morale, eventually leading to mass desertions.
On 18 September, a second Entente formation assaulted the Bulgarian positions in the vicinity of Doiran Lake. Effectively employing machine gun and artillery fire the Bulgarians managed to stall the Allied advance on the Doiran sector. However the collapse of the front at Dobro Pole forced the Bulgarians to withdraw from Doiran. The Allies pursued the German 11th Army and the Bulgarian 1st Army, while pushing deeper into Vardar Macedonia. By 29 September, the Allies had captured the former HQ of Skopje, thus endangering the remnants of the 11th Army.
The parallel development of the anti-monarchist Radomir Rebellion forced Bulgaria to sign the Armistice of Salonica and withdraw from the war. The treaty included the full capitulation of the 11th Army, bringing the final tally of Bulgarian and German prisoners to 77,000 and granting the Allies 500 artillery pieces. The Bulgarian downfall turned the strategic and operational balance of the war against the Central Powers. The Macedonian Front was brought to an end at noon on 30 September, when the ceasefire came into effect.
Prelude
The 28 June 1914, assassination of Austro-Hungarian heir presumptive Archduke Franz Ferdinand precipitated Austria-Hungary's declaration of war against Serbia. The conflict quickly attracted the involvement of all major European countries, pitting the Central Powers against the Entente coalition and starting World War I.
Serbia was defeated during the autumn 1915 phase of the Serbian campaign, prompting France and Britain to transfer troops from the Gallipoli campaign to Greek Macedonia. The Macedonian front was thus established in an effort to support the remnants of the Serbian army to conquer Vardar Macedonia.
On 17 August 1916, in the Struma operation Bulgaria invaded Greece, easily conquering all Greek territory east of the Struma, since the Greek Army was ordered not to resist by the pro-German King Constantine. The surrender of territory recently won with difficulty in the Second Balkan War of 1913 was the last straw for many supporters of Liberal Party politician Eleftherios Venizelos. With Allied assistance, they launched a coup which secured Thessaloniki and most of Greek Macedonia, causing the National Schism. In June 1917, the Venizelists gained full control of the country, immediately declaring war on the Central Powers and joining the Allied Army of the Orient operating on the Balkan Front. The Greek entry into the war along with the 24 division reinforcements that the Army had received in the spring of the same year had created a strategic advantage for the Entente.
On 30 May 1918, the Allies launched an offensive on the heavily fortified Skra salient, commencing the Battle of Skra-di-Legen. Utilizing the cover of heavy artillery a Franco-Hellenic force made a rapid push into the enemy trenches, conquering Skra and the surrounding system of fortifications. Greek casualties amounted to 434–440 killed in action, 154–164 missing in action and 1,974–2,220 wounded, France lost approximately 150 men killed or injured. A total of 1,782 soldiers of the Central Powers became prisoners of war, including a small number of German engineers and artillery specialists that served in Bulgarian units; considerable amounts of military equipment also fell into Entente hands. The plan for a Bulgarian counterattack against Skra remained unfulfilled as the Bulgarian soldiers refused to take part in the operation. Both the Greek and the French press used the opportunity to extol the efforts of the Greek army, favorably influencing the Greek mobilization.
The fall of Skra prompted Bulgarian prime minister Vasil Radoslavov to resign on 21 June 1918. Aleksandar Malinov who assumed office immediately afterwards pursued secret negotiations with Britain, offering Bulgaria's exit from the war with the condition that Bulgaria fully retain eastern Macedonia. However, British prime minister David Lloyd George rejected the proposal, assuring the Greek ambassador in London Ioannis Gennadius, that Britain would not act against Greek interests.
In late July 1918, Bulgarian commander-in-chief Nikola Zhekov sent German Field Marshal Paul von Hindenburg a message regarding a rumored Entente offensive, and detailed Bulgaria's inability to adequately defend the Vardar portion of the front. Zhekov requested that Germany immediately reinforce the Balkan Front, hinting that Austria-Hungary would also be required to strengthen its positions in Albania. On 17 August, Hindenburg pledged to provide Bulgaria with support once the situation on other front permits it. Hindenburg's reluctance to support Bulgaria was also manifested by the early September redeployment of the last German Jäger battalion stationed in Macedonia back into Germany.
The Bulgarians, using information from escaped prisoners of war, determined that Entente forces would engage in hostile actions west of lake Ohrid, in Monastir, Dobro Pole or Human. On 27 August, the 2nd and 3rd Bulgarian Divisions stationed at Dobro Pole were ordered to make emergency preparations, as new evidence indicated a frontal assault on Dobro Pole along with a secondary attack on Human. By 7 September, Dobro Pole was reinforced by one machine gun company, six infantry battalions and ten heavy howitzers, the head of Army Group Scholtz General Friedrich von Scholtz then stated that the defensive measures made the defense of the front feasible. Scholtz had failed to take into account the departure of Bulgarian chief of staff Nikola Zhekov and his subsequent replacement by Georgi Todorov. Widespread insubordination and desertions also plagued the Bulgarian troops who refused to participate in fortification works; poor rations and fatigue contributed to the low morale.
A day prior to the Entente offensive, General Louis Franchet d'Espèrey laid out the final plan for the operation. The first phase consisted of a combined Franco-Serbian attack on the positions of the 2nd and 3rd Bulgarian Divisions, which was expected to create a breach of the front line in the area of Dobro Pole, while also posing a danger to the Bulgarian supply lines on river Vardar. The Dobro Pole ("Good Field") peak dominated the region, providing excellent observation points for the defenders. Dobro Pole was surrounded by a well-developed system of trenches which, in combination with the rough terrain, made the area impassable for wheeled transport. Dobro Pole was, however, lower and less steep than the mountains on other parts of the front that averaged .
A second Anglo-Franco-Hellenic force would then attack the Bulgarian 1st Army between the Vardar river and Doiran Lake, preventing it from forming new defensive positions in the area. The initial advance would allow the Armée d'Orient to progress in support of other units first to Prilep, Disma and Borran. In the meantime, an Anglo-Hellenic force would strike Mount Belasica, occupying the Rupel Pass. The Doiran sector had previously been subject to two major Entente offensives known as the First Battle of Doiran (August 1916) and Second Battle of Doiran (April–May 1917). Both engagements ended in decisive Bulgarian victories, forcing the Allies to limit their operations to small raids and harassing fire. Between 1916 and July 1918, Bulgarian defenses around Doiran underwent a period of considerable reorganization under the personal supervision of General Vladimir Vazov. The sector was divided into two defensive areas, protected by the Mountain Division and the 9th Infantry Division respectively. Bulgaria established combat security outposts at a distance of from the enemy trenches, while also reinforcing the defenses of the dominant Dub and Kala Tepe mountains. Similarly to Dobro Pole the defenses consisted of a series of mutually supporting trenches, with built in observation posts, machine gun positions and artillery pieces.
D'Espèrey expected to march the Allied Army of the Orient through the towns of Demir Hisar, Rupel, Petrici, Blagusa, Gradec, Štip and Belessa finally seizing Skopje. Units stationed at Katsania and Tetovo would prevent a Bulgarian flanking maneuver, while the main body of the force would widen the breach both in Štip and Prilep. In case of a collapse of the front between Dobro Pole and Tzena, the Bulgarian 1st Army and the German 11th Army would either be annihilated or, in less favorable circumstances, perform an organised retreat to a new defensive line on river Crna. The prevention of such a retreat was to be achieved by a rapid, penetrating attack on Gradsko, Dren Planina and Visoka.
Offensive Battle of Dobro Pole
At 8 a.m. on 14 September 1918, Entente forces commenced a 566-gun artillery barrage on enemy positions. Their aircraft also bombed enemy positions and strafed a 250-truck column moving towards Kozjak. On the same day, Scholtz sent Hindenburg a telegraph stating that
The Bulgarian high command did not attempt to perform a spoiling attack as they lacked the necessary vehicles and pack animals. The barrage did not cause a significant number of casualties but severely affected the Bulgarian esprit de corps. On the night between 14 and 15 September, Franco-Serbian patrols reported that the artillery barrage had dealt sufficient damage to the barbed wire entanglements separating the trenches.
At 5:30 a.m. on 15 September, the French 122nd and 17th (Colonial) Divisions struck Sokol, Dobro Pole, Kravitski Kamene and Kravitsa while the Serbian Shumadia Division assaulted Kamene and Veternik. The Greek Archipelago Division, 3rd Division and 4th Division under Panagiotis Gargalidis acted as a link between the Serbian and French troops without entering combat. The offensive immediately caused a wave of mass desertion among the Bulgarian units; the remaining infantrymen and artillery squadrons were not able to hold their ground. During the course of the battle, the 122nd Division broke into two columns and suffered heavy casualties. The left column managed to reach a position located from Sokol at 6:30 a.m. and take the peak at the end of the day. At 16:00 pm, the right column captured Dobro Pole after rushing a segment of steep terrain. The 17th Division seized Kravitsa at 7:00 am, suppressing the last signs of resistance.