In "Generation Kill"...?

Question

What's the story behind "Captain America?" I've heard him talk about going to Ranger school (Rangers are an Army unit) and yet he is serving with Marines. What gives?

Answer 1

I don't know man.  The guy is generally just portrayed as a moron on that show.

Answer 2

Alot of units cross train a percentage of their ranks, only makes sense. Why invent a school when another branch already has one up and running.  

Answer 3

only a certain few of Marines get to go to ranger school.