On March 2, 1969 Soviet troops patrolling Damansky Island (Zhenbao) on the Ussuri River came under fire from Chinese troops. The attack, just 120 miles from the major Soviet city of Khabarovsk, killed fifty Soviet troops and wounded many more. Moscow believed that the attack was premeditated, with Beijing bringing in a special combat unit to ambush Soviet forces. Alleged atrocities against wounded Soviet troops made the Soviet leadership furious.
Soviet border guards counterattacked Chinese forces in and around the island on March 15, according to the CIA killing “hundreds” of Chinese troops. Clashes continued through the spring and summer, and by August, CIA director Richard Helms had informed the press that the Soviet leadership had been discreetly inquiring with foreign governments about their opinion on a preemptive strike on China.