President Barack Obama promised Haitians Thursday they would not be forgotten, offering 100 million dollars in immediate earthquake aid and the backing of every element of US power. A sweeping US military and civilian operation to aid quake-devastated Haiti kicked into high gear, with Washington sending ships, helicopters, planes, rescue teams, a floating hospital and more than 5,000 troops. 'To the people of Haiti, we say clearly and with conviction, you will not be forsaken, you will not be forgotten,' Obama said. The president offered 'every element of our national capacity, our diplomacy and development assistance, the power of our military and most importantly, the compassion of our country' following the disaster. Obama recalled two top deputies from foreign trips, with Secretary of State Hillary Clinton returning to Washington early Thursday to help coordinate US efforts after Haiti's worst earthquake in more than a century. Forward teams of civilian and military experts began landing in Haiti Wednesday as US surveillance aircraft scanned for survivors and tried to assess the damage from Tuesday's 7.0-magnitude quake. As a wealthy neighbor with the world's most powerful military, the United States appeared well-placed to lead aid efforts for the impoverished Caribbean nation, mobilizing an array of specialists and high-tech equipment. The US Army ordered a brigade of 3,500 troops deployed to Haiti to 'provide humanitarian assistance and relief and security as required,' said army spokesman Gary Tallman. They would begin to arrive late Thursday. The US military has deployed a large amphibious ship with a Marine Expeditionary Unit of about 2,000 personnel, Clinton said. 'The extent of the planning that has to go into this to make sure we do the maximum good possible is something that the United States is taking the lead in,' she said, while also praising the relief efforts by several other nations. Defense Secretary Robert Gates canceled plans for a weekend trip to Australia in order to manage the Pentagon's response, while Clinton abandoned her trip to Asia, flying back from Hawaii and warning that the quake caused a very high loss of life. 'We know it's going to be in the tens of thousands,' she told MSNBC. Early casualty figures were impossible to calculate with apparently no central Haitian authority taking control of disaster operations, but Prime Minister Jean-Max Bellerive told CNN the final death toll could top 100,000. President Rene Preval told the network 50,000 could be dead. The USS Carl Vinson aircraft carrier was en route and set to arrive Thursday, while destroyers and more Coast Guard ships were on the way, General Douglas Fraser, head of the US Southern Command, told reporters. Part of the effort was aimed at providing assistance to many of the 45,000 Americans Clinton said were in Haiti, some of whom were injured in the disaster. 'The Coast Guard has been magnificent in helping to evacuate people,' she said. The USNS Comfort, a floating military hospital with operating rooms and a team of doctors and medical supplies, was readying to sail to waters off Haiti, Clinton said. Search and rescue teams from Florida, Virginia and California were on the ground Thursday in Port-au-Prince, as was a group of US Air Force experts to restore air traffic control and communications at the airport, badly needed as a hub for international relief efforts. 'The United States is providing a lot of the glue that is keeping people communicating and working together as we try to assert authority, reinstate the government and begin to do what governments have to do to rebuild and reconstruct this damaged country,' Clinton told Fox News. About 60 US military personnel were on the ground and some 30 military engineers, medical specialists and other experts were flying in aboard a C-130 transport plane to help organize emergency aid, Fraser said. On Wednesday, a US Navy P-3 maritime patrol aircraft, usually used to track drug trafficking, flew over Port-au-Prince, and the initial survey from the air indicated the damage was mainly concentrated around the capital, but the full scale of the disaster was still unknown. 'We don't have a clear assessment right now of what the situation on the ground is,' Fraser said. US officials will also be acutely aware of the need to try to stem any mass panic or attempts to flee Haiti by sea to reach the United States. Over the years, hundreds have made the perilous 1,000-kilometer (625-mile) journey in leaky boats, and many have perished on the way. Obama said Wednesday the Defense and State departments, along with the US Agency for International Development, would lead relief efforts after the 'heart- wrenching' tragedy. 