Ushering in a new era for the US military, Defense Secretary Leon Panetta on Thursday lifted a ban on women serving in ground combat, saying female troops had proven their courage in a decade of war. The ground-breaking decision reflected the changed realities of the battlefield, Panetta said, as women soldiers already have been fighting in conflicts that lacked clear frontlines. "Female service members have faced the reality of combat, proven their willingness to fight and, yes, to die to defend their fellow Americans," the Pentagon chief told a news conference. "Not everyone is going to be able to be a combat soldier. But everyone is entitled to a chance," he said before signing a memo ending the ban. President Barack Obama, whose inauguration address on Monday promoted the idea of opening opportunities to all Americans, hailed the move as "historic" and "another step toward fulfilling our nation's founding ideals of fairness and equality." The move highlighted evolving social attitudes and marked yet another sweeping change for the American military under Obama, who led a drive to end a prohibition on openly gay troops. Panetta unveiled the decision after a months-long review by chiefs of all the armed services who unanimously endorsed a gradual change that would be phased in over the next three years. Under the decision, the armed services will have until January 2016 to carry out the new policy. Military departments would have to submit detailed plans on implementing the order by May 15, 2013, Panetta said. Panetta's decision will apply mainly to the Army and the Marine Corps, as the Air Force and Navy already have lifted most prohibitions on women in combat, allowing them to fly fighter jets and fire weapons on ships. In 2010, the Navy opted to allow women to serve on submarines. US commanders began taking a second look at the ban in 2010 to reflect the changing conditions on the battlefield, as the wars in Iraq and Afghanistan have put women in harm's way. General Martin Dempsey, chairman of the Joint Chiefs of Staff, told the same news conference that the move was part of a long-term trend in the military and that he had witnessed changes as an army division commander in Iraq. Gender-neutral criteria for combat jobs would be drafted without watering down tough standards for physical strength or other skills, he said. "The burden used to be that we would say, 'why should a woman serve in a particular specialty?' Now it's, 'why shouldn't a woman serve in a particular specialty?'" Dempsey said. And the four-star general said he and other service chiefs expected women would make it into the elite ranks of the special operation forces: "I think we all believe that there will be women who can meet those standards." A senior defence official said the change would be incremental, to allow each service to ensure a smooth transition. "With a change of this magnitude, it may take some time," the official, who spoke on condition of anonymity, told reporters. Women make up about 14.5 per cent of the active duty US military, or about 204,000 service members. And 152 female troops have lost their lives in the wars in Iraq and Afghanistan. Advocates for changing the policy have long argued that denying female troops a chance at ground combat jobs effectively blocks them from attaining top jobs as commanders. Some senior officers opposed to the change say infantry units require serious upper body strength and warned that difficult physical tests might be relaxed for female recruits. Right-leaning commentators also have questioned whether mothers in uniform -- especially single parents -- should be sent into combat, even if they volunteered. The Marine Corps recently opened up infantry officer training to women but the two females who volunteered failed to pass the gruelling test.