To lift the ban took effect am Eastern Time United States on Tuesday at 12:01.
Some in Congress still oppose change, but senior Pentagon certified it will not undermine the military's ability to recruit or fight for the war.
The abolition of DADT is one of the priorities of President Barack Obama, and unlike a lot of other things on his agenda, he pulled off earlier this year.
And President Bill Clinton tried to cancel the Army-wide ban on gays in 1993, but faced strong objections from the Joint Chiefs of Staff.
Do not ask, do not tell was issued as a compromise. Nearly two decades later, Obama Joint Chiefs of Staff on his side, and politics is out.
Army gave out a business as usual on Tuesday, saying simply: "The Law", and reminding the soldiers to treat each other to some extent.
Defense Minister Leon Panetta, chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, scheduled a news conference later on Tuesday.
At the same time, plans to a group of bipartisan supporters in Congress to allow openly gay service in the army at a news conference on Capitol Hill.
