Women serving in the U.S. Navy and Marine Corps now have the right to take 18 weeks of paid maternity leave, three times the amount they had previously.

The change is effective immediately, Secretary of the Navy Ray Mabus announced Thursday, and will apply retroactively to any woman who has been granted maternity leave since January 1, 2015.

“We have incredibly talented women who want to serve, and they also want to be mothers and have the time to fulfill that important role the right way. We can do that for them,” Mabus said in a statement. “This flexibility is an investment in our people and our Services, and a safeguard against losing skilled service members.”

The policy change will make the Navy and Marine Corps the first military services to provide more than six weeks of paid maternity leave.

A woman’s unit commander can now authorize an additional 12 weeks of convalescent leave, or sick leave, following the birth of a child. Before this policy change, only a hospital commander could authorize a service member to take more than 42 days of leave after childbirth.

Female sailors and Marines don’t have to take their leave all at once, but they do have to take it within a year after the child’s birth.

Other branches of the military require the six weeks of maternity leave to be taken consecutively. Service members are also exempt from deployment for 4-12 months after giving birth, and have the option of transferring out of active duty for 1-3 years.

New fathers will still get ten days of paternity leave, taken consecutively, for married active duty members whose spouse gives birth to a child. New adoptive parents can still take three weeks of leave.

The United States is only one of two countries, along with Papua New Guinea, that does not offer any guaranteed paid maternity leave. The Family and Medical Leave Act allows some workers to take 12 weeks of leave without the risk of losing their job, but those workers aren’t guaranteed any pay.

Other federal employees still have no official paid maternity or paternity leave, although Democrats in Congress have tried to pass legislation changing that. President Obama signed an executive order in January that lets federal workers take up to six weeks of sick time after the birth, adoption, or foster placement of a new child—but that leave is an advance on future sick time that workers would have to pay back later.

Mabus had announced in May that he hoped to double maternity leave from six to 12 weeks, as well as increase female recruitment to 25 percent from the current 18 percent in the Navy and 5 percent in the Marines.

“When the women in our Navy and Marine Corps answer the call to serve, they are making the difficult choice to be away from their children—sometimes for prolonged periods of time—so that they can do the demanding jobs that we ask them to do,” Mabus said. “With increased maternity leave, we can demonstrate the commitment of the Navy and Marine Corps to the women who are committed to serve.”