How hard is Army Air Assault Training?

I thought for a second that you had to go to airborne training to be deployed on a helicopter. I was wrong. So here is what I want to know, how hard is Air Assault training? I heard it was only 2 weeks. So it can't be too hard. And I heard it is mostly knowledge that is hard. I know about the 2 mile run and 12 mile march. But how much weight do you need to cary in the 12 mile march. Also, can a 2nd lieutenant be allowed to be an air assault soldier?