The U.S. Army is moving ahead with a major reorganization to make the brigade the major combat unit, with the division replacing the corps as a headquarters. Details of the new organization are not yet set, but active duty combat brigades will probably increase from 33 to 48 and reserve/National Guard combat brigades from 15 to 22. This makes available some 60 combat brigades, but only about 140 infantry and armor battalions. That's because the new plan calls for frequently using only two combat battalions per brigade. The idea behind that is to mix tank and infantry companies more frequently, and regularly. This is an idea that has been bounced around for decades, because in combat, you often have tank battalions broken up so the tanks can operate with infantry units. 

There is already considerable experience with "independent brigades," as the army has maintained some of these for over half a century. Artillery, engineer and other support units are added to a regular brigade (that is part of a division), and much is known about what works and what doesn't with independent brigades (that can operate by themselves without being part of a division). Artillery and aviation, however, is likely to be more centralized, and parceled out to brigades as needed by the division headquarters (just as corps have long parceled out stuff to divisions). Artillery units, especially MLRS (rocket) battalions, have sufficient range that they can easily support several widely dispersed brigades if the communications are available. Aviation, of course, has even greater range. The new organization could send a division with one to five brigades, depending on the mission. Such a division would have a strength of from 7,000-30,000 troops. The first two divisions to go through the reorganization are the 3rd Mechanized Infantry and the 101st Airborne.