At the beginning of World War I Yudenich was appointed Chief of Staff of the Russian Caucasus Army.
 Major operations included the Battle of Sarikamish, a victory against Enver Pasha of the Ottoman Empire.
In January 1915, Yudenich was promoted to General of Infantry, and replaced Count Illarion Ivanovich Vorontsov-Dashkov as commander of the Caucasus Campaign.
Yudenich tried to exploit the Turkish defeat by attacking into Turkish territory, specifically around Lake Van during the Siege of Van.
While the Russians did capture Van in May 1915, they were forced to withdraw from the city two months later.
The Ottoman 3rd Army re-occupied Van in August.

At this time, Grand Duke Nicholas, having been removed from command of all of Russia's armies, was put in charge of the Caucasus region.
Yudenich was given a free hand by the Grand Duke and, in September, the Russians retook Van and re-established the Administration for Western Armenia in June 1916.
Fighting back and forth around this region continued for the next 14 months without a clear victory for either side.

In 1916 Yudenich successfully carried out an offensive, winning the Battle of Erzurum (1916) and the Trebizond Campaign.
In the summer of that year, his forces fought off a Turkish counter-attack culminating in the Battle of Erzincan (which included the presence of Turkish General Mustafa Kemal).
During this battle, Yudenich was awarded the Order of St. George (2nd degree), the final time this decoration was awarded in the Russian Empire.

Following the February Revolution, in 1917 Yudenich was appointed commander of the Caucasus Front, but in May the Russian Provisional Government removed him from command for insubordination, and on the direct orders from Alexander Kerensky, he retired from the army.
Yudenich then relocated from Tbilisi to Petrograd, where he supported the Kornilov Revolt.
At the beginning of World War I Yudenich was appointed Chief of Staff of the Russian Caucasus Army.  Major operations included the Battle of Sarikamish, a victory against Enver Pasha of the Ottoman Empire. In January 1915, Yudenich was promoted to General of Infantry, and replaced Count Illarion Ivanovich Vorontsov-Dashkov as commander of the Caucasus Campaign. Yudenich tried to exploit the Turkish defeat by attacking into Turkish territory, specifically around Lake Van during the Siege of Van. While the Russians did capture Van in May 1915, they were forced to withdraw from the city two months later. The Ottoman 3rd Army re-occupied Van in August.
At this time, Grand Duke Nicholas, having been removed from command of all of Russia's armies, was put in charge of the Caucasus region. Yudenich was given a free hand by the Grand Duke and, in September, the Russians retook Van and re-established the Administration for Western Armenia in June 1916. Fighting back and forth around this region continued for the next 14 months without a clear victory for either side.
In 1916 Yudenich successfully carried out an offensive, winning the Battle of Erzurum (1916) and the Trebizond Campaign. In the summer of that year, his forces fought off a Turkish counter-attack culminating in the Battle of Erzincan (which included the presence of Turkish General Mustafa Kemal). During this battle, Yudenich was awarded the Order of St. George (2nd degree), the final time this decoration was awarded in the Russian Empire.
Following the February Revolution, in 1917 Yudenich was appointed commander of the Caucasus Front, but in May the Russian Provisional Government removed him from command for insubordination, and on the direct orders from Alexander Kerensky, he retired from the army. Yudenich then relocated from Tbilisi to Petrograd, where he supported the Kornilov Revolt.
Nikolai Yudenich