The US military will open up all positions - including frontline combat roles - to women, Defence Secretary Ashton Carter has announced in a sweeping move that ends centuries of men-only tradition.
The historic step trumps a Marine Corps call for a partial exemption after it claimed mixed-gender combat units were not as effective as male groups.
"There will be no exceptions," Carter said on Thursday (local time).
While acknowledging that, on average, physical differences exist between sexes, Carter said plenty of women can meet the military's rigorous physical standards for combat roles - just as there are some men who cannot.
"As long as they qualify and meet the standards, women will ... be allowed to drive tanks, fire mortars, and lead infantry soldiers into combat," Carter said.
"They'll be able to serve as Army rangers and green berets, Navy SEALS, Marine Corps infantry, Air Force parajumpers and everything else that was previously open only to men."
Given the tough physical standards, Carter stressed that equal opportunity would probably not translate to equal participation of men and women in all roles.
"There must be no quotas or perception thereof," he said.
The US military currently comprises about 1.38 million people, about 15.5 percent of them women.
President Barack Obama's administration in 2013 asked for all combat positions to be open to women by 2016, including the infantry, artillery, armour and special forces.
But Obama gave the Pentagon the opportunity to request exceptions, provided these were justified by operational constraints.
Though it was widely expected, Carter's announcement brings to a head something of a paradigm shift in how the United States views its fighting forces. It was only five years ago that gays were banned from serving openly in the military under its "Don't Ask, Don't Tell" law.
Carter, who is Obama's fourth defence secretary and started his job in February after working his way up the Pentagon's bureaucratic ranks, has spoken frequently about the need for the vast US military to be inclusive so it can attract the talent it needs.
"Our force of the future must continue to benefit from the best people America has to offer," Carter said.
"In the 21st century, that requires drawing strength from the broadest possible pool of talent. This includes women ... We have to take full advantage of every individual who can meet our standards."
The changes will be implemented "as soon as practicable" after January 2, and no later than April 1, a Pentagon memo said.
Carter's announcement was greeted frostily by senior Republican lawmakers.
"Carter's decision to open combat positions to women will have a consequential impact on our service members and our military's warfighting capabilities," Senator John McCain and Congressman Mac Thornberry, who both chair armed services committees, said in a statement.
We "intend to carefully and thoroughly review all relevant documentation related to today's decision," they added.