Operation Ring, known in Azerbaijan as Operation Chaykand was the codename for the May 1991 military operation conducted by the Soviet Army, Internal Troops of the Ministry of Internal Affairs of the USSR and OMON units of the Azerbaijan SSR in the Khanlar and Shahumyan districts of the Azerbaijani SSR, the Shusha, Martakert and Hadrut districts of the Nagorno-Karabakh Autonomous Oblast, and along the eastern border of the Armenian SSR in the districts of Goris, Noyemberyan, Ijevan and Shamshadin. Wikipedia