Over the last two years, the United States has sent over the largest helicopter force ever seen in Afghanistan. Most of the aircraft in Afghanistan are helicopters, and most of these belong to the U.S. Army. By itself, U.S. Army aviation would be one of the largest air forces in the world. The U.S. Army has 20 CABs (Combat Aviation Brigades). Twelve are active duty units, and eight are from the reserves. Another active duty CAB is being formed. A CAB contains, on average, 2,700 troops and 120 aircraft (nearly all OH-58 scout, AH-64 gunship and UH-60 and CH-47 transport helicopters). The CABs sent to Afghanistan are worked very hard. In Afghanistan, American helicopter pilots fly about 63 hours a month each. This is five times the number of hours they would fly back at their home base. The CABs are spending more time overseas than the (ground) combat brigades.
Even with the withdrawal of troops from Iraq, a record number of CABs are staying overseas. That's because helicopters are more vital, and numerous, in Afghanistan than in Iraq. There are only about 60 percent as many U.S. troops in Afghanistan, compared to peak strength in Iraq. Thus from last year to 2014, about a third of the CABs will be overseas at one time. That's fifty percent more than in the last few years. To help support that, two additional CABs were formed in the last year. One was assembled from existing helicopters not assigned to CABs, and is already in service. The other one is being built from scratch, and will be ready by the end of the year. Forming these two new CABs cost $6.6 billion. In addition to this, hundreds of heavy (1.5 ton Sky Warrior) UAVs are being added to the CABs. The army is also reorganizing the CABs, which currently come in three types; light, medium and heavy, into "Full Spectrum" units that contain a mix of different helicopter types.
Afghanistan operations use helicopters more than in Iraq, especially for getting casualties to field hospitals. These medevac (medical evacuation) choppers have to travel farther than in Iraq, where the battlefields were closer to major bases. Because of those longer distances, more helicopters are needed to deal with the additional travel times.
The CABs have come a long way in the past few decades. Current American combat divisions have 25-30 battalions assigned, with half of them being combat units. These battalions are organized into seven brigade size organizations, plus the division headquarters (which often controls the Military Intelligence battalion, Signal Battalion and several company size units.)
During the 1990s, American army combat divisions underwent some subtle changes in organization and operation. One of the more noticeable differences has been the appearance of the "fourth brigade." Since the 1960s, Army divisions referred to their "three brigades" to mean the three brigades that contained their infantry and armor battalions. But in the 1980s, the aviation battalion the divisions had since the 1960s, was expanded to an aviation brigade. In the 1990s, it became customary to assign the division reconnaissance battalion to the aviation brigade as well. This meant that a brigade that usually had a transport helicopter battalion and an attack helicopter battalion now had a ground unit (the cavalry squadron, which was a battalion size unit). In some divisions, the aviation brigade sometimes had a tank or infantry battalion assigned as well, at least for training exercises or combat operations. During the 1990s, tank and mechanized divisions were given two more engineer battalions, with the three engineer battalions now organized into an engineer brigade. Although these are combat engineers, the three battalions are usually assigned to one of the four combat brigades. There are two other "support brigades"; the divisional artillery (with four artillery battalions) and the divisional support command (with six or more support and maintenance battalions.) Manpower in US divisions now runs close to 20,000 troops with the attachment of additional artillery and aviation battalions. Sometimes yet another combat brigade is attached as well. But the CAB was always considered the most vital of these combat support units.
In the last decade, the division underwent another change, with the brigades getting more support units, and the division acting like the old corps headquarters, controlling a more varied mix of brigades (depending on the situation.) With CABs no longer just the "fourth brigade" in divisions, the number of CABs grew, and that growth continues.