Yes, that's a GAU-8 on a Patton tank. It was GE's entry in the division air defense program back in the 70s. Too bad Ford won, imagine if this beast had gone into production.
Also, discuss the VEPR and Browning Buckmark .22 (the pistol I'd chamber in 9mm and then give to my S.S. officers if I were Fuhrer. Those things are sleek)