As the title says, WI the US created a couple of Armoured Corps by putting some of their Armoured Divisions together and then grouped them into an Army. It wouldn't take much, especially since US infrantry divisions have a decent establishment of tanks and lavish transport so could be incorporated into an Armoured Corps without it losing its focus. My suggestion is 2 Corps each with one 'heavy' AD, one 'light' AD and an ID with extra half tracks and trucks and another AD as the Army 'reserve' formation. This would be the bare bones of the Armoured Army, the Army AD could be added to to make it a theird Corps if need be.
Would such an Army be handy in WW2?