Here's a pic http://www.flickr.com/photos/myfavoritepictures/5782122052/
I'm just speculating, but I think all guns traverse on the same mechanism. Ie on a gear of substantial size, precise and rugged enough to withstand the recoil and dirt and knocks about. Isn't it the only such traverse mechanism known to man, whatever you're firing?
Whether the gear is visible or not does not change the operating principle, just like whether the traverse is narrow like on the guns of old, or almost 360 degrees like on the 122mm Soviet D-30 and the 88mm Flak 18
not a turntable, it's a big horizontal gear that the gun sits on. it has teeth for rigidity to transfer the recoil into the ground beneath. traverse is not 360 deg because the trail legs transfer the recoil too.