User blog comment:Bovell/Lots of new Battlefield 3 details via Twitter, DreamHack festival, PSM3, and interview/@comment-3225377-20110626015855/@comment-28584497-20110626031045

I know they're part of the department of the Navy, but that doesn't change the fact that in general terms, they fulfill the same role, purpose, and are armed/trained in largely the same manner as infantry falling under the Army.

They're all infantry.