On 12 March , the prime minister closed the port of Sihanoukville -- through which weapons were being smuggled to the NLF -- to the North Vietnamese .
On 12 March , the prime minister issued an impossible ultimatum to them .
On 12 March , the prime minister closed the port of Sihanoukville -- through which weapons were being smuggled to the NLF -- to the North Vietnamese and issued an impossible ultimatum to them .