The only series I've read with sentient battle tanks is Bolo*. The original novels are from the 80s (by Keith Laumer), followed by a series of anthologies and a couple of stand alone novels by other authors. From your description, I suspect you read David Weber's Old Soldiers. (http://www.webscription.net/chapters/1416508988/1416508988.htm?blurb)

*OK. There is the possessed tank in Those Who Hunt Elves. But that is manga and fantasy.