1916 Russian offensive against the Ottoman Empire during WW1
The Erzurum offensive (; ) or Battle of Erzurum () was a major winter offensive by the Imperial Russian Army on the Caucasus Campaign, during the First World War that led to the capture of the strategic city of Erzurum. The Ottoman forces, in winter quarters, suffered a series of unexpected reverses, which led to a Russian victory.
Background.
After the defeat at the Battle of Sarikamish, the Ottomans tried to reorganise. The Armenian genocide made supplying their forces a problem. Trade by Armenians, which had supplied the Ottoman Army, was disrupted. The dismissal of Armenian soldiers into labor battalions and their massacres further worsened the problem. However, throughout 1915, the northern sectors of the front remained quiet.
At the same time, the end of the Gallipoli Campaign would free up considerable Turkish soldiers, which made Nikolai Yudenich, the commander of the Russian Caucasus Army, prepare to launch an offensive. He hoped to take the main fortress of Erzurum in the area, followed by Trabzon. That would be was a difficult campaign since Erzurum was protected by a number of forts in the mountains.
Eight of the available Ottoman divisions were designated for the Caucasus Front. Yudenich believed that he could launch an offensive before the Ottoman divisions could be redeployed and readied for battle.
Forces.
Russian.
The Russians had 130,000 infantry and 35,000 cavalry. They also had 160,000 troops in reserve, 150 supply trucks and 20 planes of the Siberian Air Squadron. According to other sources, the attacking group (the Russian Caucasian army) included about 120 thousand people and 338 guns.
Ottoman.
The Ottoman forces had 78,000 troops in the region.
Operations.
The Ottoman High Command did not expect any Russian operations during winter. Mahmut Kamil was in Istanbul, and his chief of staff, Colonel Felix Guse, was in Germany. General Yudenich launched a major winter offensive. 
Defense lines.
The Russians concentrated a little more troops on the strike directions, aerial reconnaissance was conducted and accurate data on the positions of the Turkish troops were collected.
The Erzurum fortress was considered impregnable, it had excellent shapes, and the road to the city passed through incredible slopes.
Road to Erzurum.
On December 29, the Russians went on the offensive in several positions at the same time, the shooters moved slowly and completely in the snow on the mountain tops, and the Turks defended very fiercely. On December 31, there was a Christmas assault on the Azapkei positions, as a result of which the Turks fled. The assault cost the Russians dearly, the 153rd Baku regiment lost up to 2,000, which is equivalent to its regular strength.
Russian penetrated into the Passinsky valley after the capture of the Azapkei positions and took Keprikey from a raid, it was a heavy defeat for the third army, but the operation had to continue and the Russians reached the outskirts of Erzurum.
On January 29, Mahmut Kamil Paşa returned from Istanbul. He could feel that the Russians would not only attack Erzurum but also renew the offensive southern flank around Lake Van. Hınıs, to the south, was taken on February 7 to prevent reinforcements from Muş from coming in. Mahmut Kamil tried to strengthen the defensive lines. That drew most of the Ottoman reserves and diverted their attention away from the decisive attack farther north. 
On February 11 and 12th, the Deveboynu Ridge, an important artillery platform, was the scene of heavy fighting. North of the Deveboynu Ridge, the Russian columns approached over the Kargapazar Ridge, which the Ottomans had considered impassable. The X Corps guarded that sector of the line, and its commander had positioned his divisions so that they could not support one another. Mahmut Kamil had five divisions in the Deve-Boyun ridge area but was slow to react to events north of that position.
The proximity of the disruption of the assault.
After a major victory, Yudenich did not plan to stop the offensive, but Grand Duke Nicholas sharply opposed this, considering the assault doomed and irrational. To force Yudenich to stop, he sent Maslovsky to him, but he supported the decision of the assault, despite the highest morale of the troops. 
Looking at this, the Grand Duke and Yudenich decided to discuss it personally, and Yudenich won the dispute, preparations for the assault began.
City of Erzurum.
The fortress was under Russian threat, both from north and east. With the victories, the Russian Army had cleared the approaches to Erzurum. The Russians were now planning to take Erzurum, a heavily-fortified stronghold. Erzurum was considered as the second best-defended town in the Ottoman Empire. The fortress was defended by 235 pieces of artillery. Its fortifications covered the city on a 180° arc in two rings. There were eleven forts and batteries covering the central area. The flanks were guarded by a group of two forts on each flank. The Ottoman Third Army lacked the soldiers to adequately man the perimeter.
On January 28, the headquarters of the Army of the Caucasus was assembled, most of the officers were in favor of postponing the assault, and Yuderich agreed with them, saying to storm 5 minutes later than planned.
On January 29, the assault on the fortress began, the Turks defended themselves and preferred to die, but did not retreat and launched counterattacks.
The breakthrough through the Kargabazir plateau was decisive, because of its loss the entire Turkish front collapsed, five days later the assault ended with the capture of the fortress.
In total, 12,988 prisoners, 12 banners and 323 guns were taken in the fortress. The battle is also considered one of the best operations of the First World War and the heaviest defeat of the Turks.
Meanwhile, remnants of the X and XI Corps established another defensive line, 8 km east of Erzurum.
Casualties.
The Ottoman troops suffered heavy losses, the 3rd army was drained of blood so much that it actually turned into a corps, by the end of 1916, the forces of the 3rd army numbered 36,000 people. The total losses of the Ottomans during the campaign is 66,000 killed, wounded and captured
Aftermath.
The battle ended with the complete defeat of the 3rd Turkish army, after the operation it ceased to exist as a single unit.
This operation showed the superiority of the Russians in the Caucasus, and their preparation for the difficult conditions there, as the battle took place in a mountainous area at a minimum temperature.
The capture of Erzurum opened the way for the Russian Army to advance deep into Anatolia.
In literature.
The Battle of Erzurum forms the climax of John Buchan's novel "Greenmantle".
References.
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