Here is the USMC Rifle Squad organization. Suhiir has done a great job putting together the USMC OOB as evidenced from the squad organization graphic.
I would add one change in adapting this org in our game. I would increase the number of men in the lead unit from four to five to similar the Squad Leader in the Rifle Squad formation. And, I would change the weapons depending on the mission, and that kinda goes without saying.