In April 1915, the 1st Expeditionary Force under the command of Halil Bey moved towards northern Persia. The objective was the city of Dilman, and to clean this region from Nazarbekov's forces, which would provide a significant tactical advantage in the Caucasian Campaign. Diliman was the place of one of the fiercest battles between the Armenians and the Turks. The first battalion of the Armenian volunteers, under the command of the Andranik repulsed the attacks of Khalil Bey, until the Russian Chernozubov arrived The newly arrived Russian forces from the Caucasus, they were able to put to flight Khalil Bey. A poorly executed night raid on April 14 cost Halil Bey around 2,000 casualties. He lost 3,600 soldiers in the course of those three days. General Nazarbekov managed to push Halil Pasha regulars towards Başkale after the Battle of Diliman (April 15, 1915), securing the situation. Halil Bey received the following cable from Enver Pasha and leave this theater of war: "Van is silenced. Roads to Bitlis and Iraq are under danger. In order to avoid even greater threats, withdraw as soon as possible and join the Third Army which would take control of these gateways." On May 8, 1915, one of the twelve Armenian messengers from the Siege of Van had got through to Persia An Armenian volunteer unit with Andranik, along with 1200 men, and commander Chernoroyal's division dispatched toward the Bashkaleh. On May 7, they captured Bashkaleh. This group from Persia reach the City of Van on May 18. They had expected to find Van still in a state of siege and were amazed at finding it in the hands of the Armenians. When word got to Yudenich, he sent a brigade of Trans-Baikal Cossacks under General Trukhin. With Van secure, fighting shifted farther west for the rest of the summer. During July 1915, Russian forces at the Caucasus Campaign had a general retreat which one Russian column retreated up to Persian frontier. This retreat was the consequence of events at June 1915. Yudenich planned an attack to limit the Ottomans at Moush and Manzikert. He planned to outflank from Beyazit and Iranian Azerbaijan towards Van. However, the Russian advance toward the Caucuses campaign did not last long. The Russian forces suffered reverses. The command of Khalil Bey Eleven divisions of regular troops attacked the very center of the Russian Caucasian advance.