In early 1964, Sihanouk signed a secret agreement with North Vietnam and the Viet Cong, allowing Chinese military aid meant for them to be delivered through Sihanoukville's port. In turn, the Cambodian army would be paid for delivering food supplies to the Viet Cong, and at the same time skim off 10percent of all military hardware supplies. In addition, he also allowed the Viet Cong to build a trail through eastern Cambodia, so that their troops could receive war supplies from North Vietnam. The trail later became known as the Sihanouk Trail. When the US learned of Viet Cong presence in eastern Cambodia, they started a bombing campaign, spurring Sihanouk to sever diplomatic ties with the US in May 1965. As a result of this secret agreement, Communist countries, including China, the Soviet Union, and Czechoslovakia, provided military aid to Cambodia.