B 47E had a twin barrel 20MM cannon that was operated by the co-pilot. They were operated by servo motors in the tail section. Every 5th round was a tracer. The Brass once decided the crews needed to experence what it was like to jettison the drop tanks. So all the crews got to go over the ocean and try it. Then they would shoot the tanks on the way down. Boom. I was only around E models so don't know what others might have had.