The top ranking US officer Mike Mullen says the end of the ban on openly gay troops, known as 'Dont Ask, Don't Tell,' will promote a sense of honour and integrity.
The American military opened the way to gays serving openly in uniform as the top ranking US officer said the historic change would promote a sense of honour and integrity.
The prohibition on openly gay troops expired at one minute after midnight on Tuesday, following years of legal challenges that date back to the 1970s.
Admiral Mike Mullen, whose passionate appeals to senators proved crucial in the repeal of the ban, told reporters the milestone would bring the military in line with its own cherished values.
"And today, with implementation of the new law fully in place, we are a stronger joint force, a more tolerant joint force, a force of more character and more honour, more in keeping with our own values," Mullen said.
The four-star admiral, chairman of the Joint Chiefs of Staff, said he had argued for repeal last year at a Senate hearing because he saw it as "a matter of integrity".
He said the prohibition "was fundamentally against everything we stand for as an institution to force people to lie about who they are just to wear a uniform".
President Barack Obama had pledged to end the ban and in December, his allies in Congress voted down the "Don't Ask, Don't Tell" law, which required gay and lesbian troops to keep their sexual orientation secret or else face dismissal.
About 14,000 service members were discharged under the law, a compromise struck in 1993 after commanders and politicians rejected former president Bill Clinton's bid to allow gays to serve openly.
Former service members who had been forced out of the military under the rule celebrated the milestone on Tuesday, with many hoping to return to the force.
Others currently in uniform voiced relief and openly declared their homosexuality, including 101 men and women who appeared in a photo essay in Outserve magazine.
In Vermont, Navy Lieutenant Gary Ross marked the new era by taking his wedding vows with his partner after the stroke of midnight, a same-sex union that would have sabotaged his military career under the "Don't Ask, Don't Tell" rule.
Even with the end of the ban, partners of gay troops under federal law will be denied benefits enjoyed by heterosexual couples, including the military's generous medical coverage.
Once the repeal was approved by politicians, the military revised policies and worked to ensure a smooth transition, with more than 97 per cent of the 2.3 million force undergoing training since January.
Defence Secretary Leon Panetta said the military was ready for the change and that the repeal was in keeping with the country's core values of "equality, equal opportunity and dignity for all Americans".
Panetta also suggested he was open to reviewing a prohibition on women in combat, a rule that has often been ignored in wars in Afghanistan and Iraq where there are no clear front lines.
In eastern Afghanistan, American soldiers at a mountain outpost said allowing openly gay recruits to serve would have scant effect on their gruelling fight against insurgents.
Captain Michael Kolton, the officer in charge at COP Monti, insisted they were "not going to have any issues" with attitudes at the base, despite the "macho" image of infantrymen.
If necessary, "they will adjust their moral values to be professional. That's what makes us disciplined infantry soldiers", he said.
"If you tell someone they're going to be tolerant they will be, better than anyone else."
Before Congress approved scrapping the ban, the Pentagon carried out a survey that showed most service members did not expect repeal to cause any major disruption.
Out of all the services, members of the Marine Corps voiced the most reservations and the commandant said before the repeal was passed that it could cause "distraction" for troops in combat.
But one Marine officer, writing in Tuesday's Washington Post, objected to General James Amos' remarks.
"Given the number of gay Marines in combat, this comment was deeply hurtful," wrote Major Darrel Choat.