Tanks, armored personnel carriers and mounted rocket launchers Thursday were driven on massive trucks up Cambodia's Highway 4 from the deep-water port of Sihanoukville towards Phnom Penh, adding to the tension that is gripping the capital. Asked what the heavy weapons might be used for, Defense Minister Tea Banh was quoted as saying, apparently facetiously: "You don't have to wonder, they will not be used to plow the rice fields. Instead, they will be used to protect the country, and crack down on anyone who tries to destroy the nation."