PARRIS ISLAND, S.C. — Stretched above the main boulevard on this historic training base in the Mid-Atlantic marsh is a white and black-lettered sign: WE MAKE MARINES.

The sign has been there for years, often serving as a snapshot backdrop for families arriving to watch their recruits graduate from boot camp after 13 weeks of mentally and physically exhausting training.

But in recent months, as lawmakers have pushed the Marine Corps to combine men and women in the same training platoons, just how the Corps will make Marines is the latest struggle for its identity.

The proposal to place men and women in the same platoons at boot camp, already well-practiced in other military branches but long resisted by the Marines, is only one part of the service’s move toward gender integration and follows the opening of combat arms schools and units to women.