Female sailors and Marines now can take 18 weeks of maternity leave. Secretary of the Navy Ray Mabus issued a directive authorizing the change July 2, which took effect immediately. Maternity leave had been limited to six weeks. The change applies retroactively to “any woman who has been authorized convalescent leave following the birth of a child since Jan. 1,” the Navy said. While new mothers do not have to take all 18 weeks of leave at once, they must use the all of the leave within a year of the birth.