The US policy banning gays from serving openly in the military ends on Tuesday, and the Pentagon says it is prepared for the change.
President Barack Obama last December signed legislation to repeal the policy known as "Don't Ask, Don't Tell," which had been passed by Congress and signed into law in 1993 under then-President Bill Clinton.
"This is not a surprise. We're prepared. People will know exactly what do in conjunction with repeal," Pentagon spokesman George Little told reporters on Monday.
Military recruiters are now accepting enlistment applications from openly gay people, Little said.
Last week, the Pentagon said 97 per cent of the military has undergone training in the new law.
The law had allowed gay men and women to serve in the military only if they kept their sexual orientation a secret.
A leading advocate, House Minority Leader Nancy Pelosi, said on Monday that the repeal is overdue.
"Our nation will finally close the door on a fundamental unfairness for gays and lesbians, and indeed affirm equality for all Americans,'' the California Democrat said.
Meanwhile, gay rights groups were preparing a series of celebrations.
Service members Legal Defence Network said repeal supporters would hold "Repeal Day'' celebrations across the country on Tuesday.
"Through these events taking place in every state across the country, we will pay tribute to their service and sacrifice as we look forward to this new era of military service - an era that honours the contributions of all qualified Americans who have served and wish to serve,'' Aubrey Sarvis, an Army veteran and executive director of the advocacy group, said.
Existing standards of personal conduct, such as those pertaining to public displays of affection, will continue regardless of sexual orientation.
There will also be no immediate changes to eligibility standards for military benefits. All service members are already entitled to certain benefits and entitlements, such as designating a partner as one's life insurance beneficiary or as designated caregiver in the Wounded Warrior programme.