 In September 1970, Khmer Rouge forces together with units of the People’s Army of Vietnam (PAVN) 1st Division, had closed this line of communications by occupying the Pich Nil Pass ().Several FANK outposts on Route 4 had been overrun in the process and other posts had been evacuated without resistance.Although the Mekong River supply route was open, Route 4 was very important to the FANK and to the Cambodian Government for all types of supplies, but particularly for military equipment.