SURGE ARITHMETIC….As everyone knows, Defense Secretary Robert Gates announced today that regular Army units would begin serving 15-month tours in Iraq instead of their usual 12-month tours. But just in case the connection to the surge isn’t obvious to everyone, here’s how he explained it:

Gates said the change is necessary to prevent five Army brigades from deploying to combat before they complete a desired 12-month rest period at home and to give predictability to soldiers and their families.

….He said the longer deployments also will allow President Bush’s “surge” strategy in Baghdad to last a year in case such high force levels are needed in Iraq.

The surge, of course, consists of five brigades. What Gates is telling us is that the Army didn’t have those brigades, and the only way they got them was by lengthening the normal tour of duty in Iraq to 15 months.

It’s not plausible that the Pentagon didn’t know this when the surge was announced. They just decided not to announce it at the time. I’ll leave it as an exercise for the reader to guess why.