In February 1949, Albania gained membership in the communist bloc's organization for coordinating economic planning, the Council for Mutual Economic Assistance (Comecon). Tirana soon entered into trade agreements with Poland, Czechoslovakia, Hungary, Romania, and the Soviet Union. Soviet and East European technical advisers took up residence in Albania, and the Soviet Union also sent Albania military advisers and built a submarine installation on Sazan Island. After the Soviet-Yugoslav split, Albania and Bulgaria were the only countries the Soviet Union could use to funnel matériel to the communists fighting in Greece. What little strategic value Albania offered the Soviet Union, however, gradually shrank as nuclear arms technology developed.