From the climactic scene in The Dark Knight Rises:
The cops are approaching two tumblers. The batcopter swoops in, does something to the tumbler on the left, then leaves.
Oddly, the screenplay indicates that he "blasted" both tumblers, not just the one.
The Tumblers fire into the line of Cops, throwing men into the air, screaming. The line of Cops is about to scatter – whoooshhh. The Bat drops down in front of the Cops and blasts both Tumblers, flipping them sideways.
The Bat rises and the Cops run towards the Mercenaries, firing – until they are close enough to fight hand-to-hand. The street is filled with thousands of men in pitched battle.
And in the film's official novelisation the tumblers were supposed to flip over and explode a bit.
Then, out of the sky, the Bat came swooping over the street. Its own cannons targeted the tumblers, blasting away at them. The armored vehicles flipped over onto their sides, smashing down on the sidewalks. Smoke and flames rose from the mangled metal. Their wheels spun uselessly in the air.
As far as I can tell, what should have been a massacre on both sides seems to have been dramatically toned down, presumably to make the film less bloody and hence to lower its censorship rating.
He disables the turret on the left tumbler, which was tracking the approaching mob. The other two tumblers don't seem to be engaged in 'turret mode'.
While stored, the heavily armored turret has a protective boot that covers the business end. Nothing gets in; nothing gets out :
The turret may have only been momentarily damaged, but Batman's intent was achieved: (a feint) provide covering fire (some of which was for effect), and at the same time provide a distraction using himself as bait to draw enemy fire away from the crowd.
The other two tumblers not having their turrets deployed, are neither a threat nor a target. Except for the one in the middle that was directly facing the crowd, as tumblers do have forward firing machine guns...
Thankfully, henchmen aren't known for RTFM.