Can anyone explain to me how US combat infantry units are organized?  

For example, how many individuals make up a squad, what rank leads the squad?  How many squads make up a platoon and what rank leads the platoon?  How many platoons make up company and what rank leads the company? How many companies make up..... etc.

Also, is this organization same for Army and Marine combat infantry units?

[url]www.marines.com[/url]

There army and the Marines are slightly different.

The basic unit is the fire team with four men; leader/grenadier, saw gunner/automatic riflemen, pointman and assistant/automatic riflemen.  In the Marines there are 3 fire teams in a rifle squad, the army uses 2 fire teams in a squad.  The fire team is lead by a squad leader, in the Marines it is suppose to be a sergeant, but often filled by lower ranks, the Army may use staff sergeants, but than again are often filled by lower ranks,

In the Marines 3 squads make up a platoon, this is commanded (led in the Army) by a Lt (either 2nd or first, the Lt has  a Platoon Sgt to assist him and possibly a messenger/RTO/Guide.  In the army there also is a weapons section of Machine guns normally in kept in the rifle platoons.

3 maneuver platoons and weapons platoon make up a Rifle company, this is commanded by a Captain.  He has a 1stSgt, XO (senior Lt), Company Gunny (in the Marines) and a few other enlisted Marines to run the company.  The weapons Plt is were the Marines keep the machine-guns, bunker buster, and mortars. The Army normally has the mortars as part of the company HQ and the other weapons down at the Plt level.

3 line (letter) companies, a Headquarters and service company and a weapons company make up a Battalion in the Marines.  It is commanded by a LtCol, who has a whole staff of Majs, Capts and Lts to assist in the running of the Battalion. The Marine Wpns Company has the BN mortars, Heavy guns and AT weapons.  The Army normally has the 3 line companies plus an AT company while it places its mortars in the HHC.    

3 or more BN make up a Regt in the Marines and Brigade in the Army.  This is commanded by a Col.

Above the Regt/BDE level is the division, commanded by a MajGen, he has at least 2 Rgt/Bdes (normally 3) and numerous support elements.

STLRN:

Thanks for that info.

I'm trying to get some accurate information for my Swedish co-work's 14 yrs old son who needs it for his school work.