The U.S. Army has a bit of a communications problem with new buzzwords used to describe its current, and quite radical, reorganization. Combat divisions are being reorganized from the current three brigades each, to having five. Moreover, many division support troops are being transferred  to the brigades. The division, instead of commanding and supporting its brigades, will mainly command a variable number of semi-independent brigades. 

All this is being hailed as a major revolution in military organization and combat. To reflect this, the new brigades are being referred to as UA (Units of Action) and the new divisions as UE (Units of Engagement.) Actually, the terms used by the people who invented all of this are UEx and Uey. But heres were it gets interesting. Those terms were not intended to replace the traditional tags, brigade and division. The army force design people who developed this stuff came up with UEx and UEy for internal use only at places like TRAC (TRADOC Analysis Center). TRADOC is the Training and Doctrine command, which comes up with the details of how the troops should operate in combat, and train to get ready for that. The force design team at TRAC needed new terms so they would know  whether they were talking about the old brigades or the new brigades.

When the brass accepted the new concepts, the new terms were again used to help explain the old brigades/new brigades to officers and troops. Thats when things got out of control. Everyone began using the UA (Units of Action)/UE (Units of Engagement) terms. It became sort of, well, cool. UA/UE are not meant to replace brigade/division, and the clumsiness of the terms UA/UE will probably see to that in the long term.

But theres more to all this than just some new names. The term "brigade" has gone through a lot of changes in the last two centuries. During World War II, the units that served as the models for the brigades in the current ROAD (ReOrganized Army Division) divisions were first called "Combat Commands." That was an official name change, and it didn't last, with the term "brigade" being restored when the current ROAD organization was implemented in the early 1960s.

All this talk of UA and UE has a deja vu air about it, as the new "independent brigade" was a very common form of organization for the Germans (as "kampfgruppe") during World War II (but mostly on the Russian front, largely out of sight of Americans). The German divisional TO&Es (tables of organization and equipment) at the end of the war looked remarkably like the proposed new UA brigades. The German organizations were based on extensive tactical experience. During World War II, the Germans came to frequently use an improvised kampfgruppe (battlegroup) system that was turned into new unit organizations towards the end of the war. Many of the German ideas were adopted by the Russians when they reorganized their army after World War II. 

The German World War II ideas have been rattling around the Pentagon since the 1960s, but aside from a few military history buffs familiar with the success of the kampfgruppe system, it didn't register much at all.

For the last few decades, there have been many attempts to establish "brigade centric" armies. The Russians had a lot of practical experience with independent brigades during World War II, and were considering going this way again towards the end of the Cold War. 

Bottom line is, it don't matter what you call it, it does matter what you do with it.