at precisely 09:00 (local time) on 9 may, six us navy a-7 corsair iis and three a-6 intruders from the uss "coral sea" flew into haiphong harbor and dropped thirty-six 1,000-pound mark-52 and mark-55 naval mines into its waters. they were protected from attacks by north vietnamese mig fighter aircraft by the guided-missile cruisers and , with several destroyers including the guided-missile destroyer launching operation custom tailor, and by supporting flights of f-4 phantoms. the reason for the precise timing of the strike became apparent when president nixon simultaneously delivered a televised speech explaining the escalation to the american people: "the only way to stop the killing is to take the weapons of war out of the hands of the international outlaws of north vietnam.". the mines were activated five days after their delivery in order to allow any vessels then in port to escape without damage. over the next three days other us carrier-based aircraft laid 11,000 more mines into north vietnam's other secondary-type harbors, effectively blockading all maritime commerce for the country.