GUANTANAMO BAY NAVAL BASE, Cuba — Defense Secretary Jim Mattis chose an unusual site Thursday to begin a preholiday tour of military bases, urging troops on this Navy base to set a good example for politically divided Americans and be always ready for war. He gave no hint about the future of Guantanamo Bay as a prison for terror suspects, and did not visit the detention center, which President Barack Obama tried unsuccessfully to close. Mattis, the first defense secretary to visit the base since Donald H. Rumsfeld in January 2002, shortly after the first prisoners arrived from Afghanistan, said the main goal of his trip was to offer holiday cheer and let the troops know their work is appreciated. He also made a point of defending the way prisoners have been treated at Guantanamo Bay, which has been called an infamous torture center. "I am confident that we’re doing the right thing here," he said. He recalled a conversation early this year with a woman, whom he did not name, who told him Guantanamo Bay was "a blot on our nation," but when invited to accompany him to the detention center for an unannounced visit, she declined. "That shut her up. She didn’t have anything more to say to me," he said. Mattis wanted to buck up the troops at Guantanamo and at Naval Station Mayport, near Jacksonville, where he visited later Thursday. He was accompanied by an Associated Press reporter and is planning today to visit Marines at Camp Lejeune, N.C., and soldiers at Fort Bragg, N.C. The troops he saw on Thursday seemed most curious about what some are calling the road to war with North Korea, whose nuclear weapons the Trump administration says pose a grave and intolerable threat. In a series of talks with troops throughout the day, North Korea came up time and again, mostly from the troops. Each time, Mattis said the focus is on finding a diplomatic solution with the help of China, Russia and others. But he also made no bones about what might happen if the diplomats fail. "If we have to do it (militarily), we expect to make it the worst day in North Korea’s life," he said, adding that if war comes, "every submarine he’s got is to be sunk and every ship he’s got is to be sunk," he said, referring to Kim Jong Un, the young North Korean leader who has threatened to use his nuclear weapons on the United States Mattis said he gets asked about the North Korea problem everywhere he travels. He said he plans on attending a meeting in Vancouver, British Columbia, next month of foreign ministers of the countries that jointly fought the 1950-53 Korean War. He said he will brief them on the situation in Korea. "When I leave, we leave this in the diplomats’ hands."