After direct American intervention in 1965, the increased presence of U.S. naval vessels in coastal waters under Operation Market Time nullified the seaborne route into South Vietnam. Following on the agreement between Sihanouk and the Chinese, an arrangement was also struck between the prince and the North Vietnamese government. In October military supplies were shipped directly from North Vietnam on communist-flagged (especially of the Eastern bloc) ships to the Cambodian port of Sihanoukville, where that nation's neutrality guaranteed their delivery. The supplies were unloaded and then transferred to trucks which transported them to the frontier zones that served as PAVN/VC base areas. These base areas also served as sanctuaries for PAVN/VC troops, who simply crossed the border from South Vietnam and then rested, reinforced, and refitted for their next campaign in safety. None of this could have been accomplished without the acquiescence of Sihanouk.