U.S. President Obama, speaking in Darwin, Australia, where U.S. Marines will begin rotations in 2012, celebrated the 60-year U.S.-Australia alliance. \"All of you are the backbone of our alliance,\" Obama told an audience of Australian troops and U.S. military in a hangar at the Royal Army Air Force Base. The centerpiece of Obama\'s two-day visit to Australia was the announcement the United States would station military forces in Darwin. Beginning with about 250 Marines in mid-2012, the U.S. presence will expand to about 2,500 troops in several years. After his speech in Darwin, Obama traveled to Bali, Indonesia, for a summit of Southeast Asian countries. \"[Our] alliance is rooted in the bonds between our people, and the democratic values that we share and our commitment to stand with each other through thick and through thin, no matter what,\" including Iraq, Afghanistan and other theaters of war, Obama said told the military and civilian audience in Darwin. He noted how troops fought hard in 1942, when Darwin was hit hard by Japanese forces in \"Australia\'s Pearl Harbor.\" \"Against overwhelming odds, our forces fought back, with honor and with courage,\" Obama said. \"Some thought Australia might fall. But we dusted ourselves off. We picked ourselves up. We rebuilt. And thanks to the extraordinary generation of troops, we went on to victory … .\" He and Prime Minister Julia Gillard paid respects to the war dead at the Australian War Memorial and the USS Peary, one of the battleships lost in battle. Going forward, the alliance has the same purpose as it had 60 years ago, \"the preservation of peace and security,\" said Obama, the first U.S. president to visit the Northern Territory.