In November 1915, Colonel Pessian as commander of Gendarmerie in Hamedan launched an attack on the pro-Russian Persian Cossack Brigade at the Battle of Musalla. His gendarmes managed to disarm the Persian Cossacks and he managed to win some of the cossacks to join his forces in a patriotic speech he made to them after their defeat. After this victory, Russians advanced on the Persian Gendermerie, in Robat-i-Karim forces under Mohammad-Hossein Jahanbani and in Hamedan-Kermanshah road forces under Colonel Pessian and Azizollah Zarghami (fa) could not defend Hamedan against an advancing Russian Caucasus Army which was superior in numbers and weapons. In Soltanabad, gendarmerie force under Masoud Kayhan (de) were also defeated by the Russians. The gendarmes then retreated to Kermanshah. On November 10, 1915, pro-Central powers Persian Gendarmerie under Ali Quli Khan Pasyan defeat pro-British Khamseh tribal forces of Ibrahim Khan Qavam-ul-Mulk (fa) and capture Shiraz. All British residents of Shiraz are arrested. Gendarmes also capture Yazd and Kerman.