The Royal Air Force has become the first branch of the British military to open up every role to men and women.
From today it will accept applications from women to join the RAF Regiment - its ground-fighting force.
The move follows a decision last year to lift the ban on females serving in close combat roles.
The main role of the 2,000-strong RAF Regiment, which sustained casualties in Afghanistan, is to patrol and protect RAF bases and airfields.
With women making up just 10% of the air force as a whole, there is unlikely to be a flood of applications, says BBC defence correspondent Jonathan Beale.
But, he adds, it is a significant moment because it means women can now apply for any RAF role, from fighter pilot to ground support.
The RAF's women will not be the first allowed to serve in close combat roles, as some recently joined the Royal Armoured Corps.
Ahead of schedule
But it will be another year before women can apply to enter army infantry units and the Royal Marines, where the physical demands can be tougher.
The ban on women serving in close combat units was lifted by then Prime Minister David Cameron in 2016.
In July, Defence Secretary Sir Michael Fallon announced that the RAF Regiment would be open to them from September - ahead of its original 2018 schedule.
He said at the time: "A diverse force is a more operationally effective force.
"Individuals who are capable of meeting the standards for the regiment will be given the opportunity to serve, regardless of their gender.
"This is a defining moment for the RAF."