[Suhiir]

Yep, already in the game.
Took a while some reliable information on their unit organization.

And NO ... they're not even close to SEALs.
Their primary function is to provide combat muscle when needed should someone like SEALs or Green Berets locate a juicy terrorist target that's just too much for them to handle with one of their standard raid type missions.

For example: The infamous incident in Mogadishu involving US Army Rangers that became the movie "Black Hawk Down" is just the sort of thing MARSOC is intended to do. While US Army Rangers are good troops they're not as well trained and equipped for urban warfare or counter-terrorism as MARSOC.