In most games and literature today the "space marine" is form of drugged up or augmented super space soldiers using the highest tech the sci fi setting has. If the marine isn't augmented themselves they often have high-tech armor that increases their stats.You're assuming 40k then? They haven't quite trademarked the term "space marine" yet.
Or maybe they have. I quit paying attention when they changed the names of everything for depressing business reasons. Still a big fan of the setting though.
Warhammer, Starcraft, Halo, Mass Effect do this.
Then you get things like Star Wars where they cheat by simply cloning a high stat character and making a ton of them