Hampering bombing runs against rebel bases like COSVN was the assistance provided by Soviet ships in the Pacific. Soviet ships in the South China Sea gave vital early warnings to NLF forces in South Vietnam. The Soviet intelligence ships detected American B-52 bombers flying from Okinawa and Guam, and relayed their airspeed and direction to COSVN headquarters. COSVN used this data to determine probable targets, and directed assets along the flight path to move "perpendicularly to the attack trajectory." While the bombing runs still caused extensive damage, the early warnings from 1968-1970 prevented them from killing a single military or civilian leader in the headquarters complexes.