It is the latest deployment in what has become the largest National Guard mobilization of its kind since the Vietnam era, according to NPR radio.

Since 9/11 terror attacks in 2001, nearly a quarter-million National Guard troops across the country have been mobilized.

The majority of National Guard infantry brigades (roughly 3,000 soldiers each) have deployed to Iraq or Afghanistan.

Now, four of those brigades with over 12,000 troops are heading out again.

The latest deployment will start sometimes December and continue on into early 2008.

The deployment is scheduled to last a year, but judging by earlier rotations, that timeframe will likely be extended.

The Pentagon said the deployments are routine rotations and have nothing to do with the Bush administration's troop-boost plan for Iraq.

But the latest announcement underscores the shortage of combat manpower in the Army at a time when the Bush administration wants to maintain at least 160,000 troops in Iraq for the foreseeable future.

In that sense, the Pentagon desperately needs manpower but it does not have enough.

As a result, the stopgap solution, at least from the Pentagon's perspective, is to use so-called "citizen soldiers" -- National Guard troops.