Mayor Daley -- a harsh critic of the proliferation of guns in society -- said Saturday it was "not a difficult decision'' to make assault rifles available to rank-and-file officers.

[ www.suntimes.com/news/metro/918254,CST-NWS-daley27.article ]

From Wikipedia:

The M4 and variants fire 5.56x45mm NATO ammunition and are gas-operated, air-cooled, magazine-fed, selective fire firearms with a 4-position telescoping stock. Original M4 models had a flat-ended telescoping stock, but newer models are now equipped with a redesigned telescoping stock that is slightly larger and the end has a curvature.

As with many carbines, the M4 is handy and more convenient to carry than a full-length rifle. While this makes it a candidate for non-infantry troops (vehicle crews, clerks and staff officers), it also makes it ideal for close quarters combat (CQC), and airborne and special operations. It has been adopted by United States Special Operations Command (USSOCOM) and is the preferred weapon of the U.S. Army Special Forces and Navy SEALs.

The M4 was developed and produced for the United States government by Colt Firearms, which has an exclusive contract to produce the M4 family of weapons through 2009; however, a number of other manufacturers offer M4-like firearms. The M4, along with the M16A4, has mostly replaced M16 and M16A2 firearms; the U.S. Air Force, for example, plans to transition completely to the M4 Carbine. The M4 has also replaced the M3A1 submachine gun that remained in service (mostly with tank crews). The M4 is similar to much earlier compact M16 versions, such as the 1960s-era XM177 family.