Just background on the region:

"Geographically, Turkey straddles the boundary dividing Europe and Asia. Sitting astride the Dardanelles and the Bosporus, Turkey controls the warm-water naval access of Russia, the Ukraine, and the Commonwealth of Independent States (CIS). Control of the straits between the Black and the Mediterranean Seas has long been a matter of keen interest to Russia, as well as other nations bordering the Black Sea. Historically, Russia has viewed such control as the sine qua non of its own sovereignty."

a href="http://www.globalsecurity.org/military/world/naval-arms-control-1936.htm">Montreux Convention