Many years ago, while attending the Artillery School at Ft. Sill, a group of us were hauled out to one of the ranges, where sat the biggest piece of ordnance the US Army ever had. A 240 mm "Big Annie" atomic cannon, which was demonstrated to us, using conventional ammo, of course, and we allowed to "pull the lanyard" which I vaguely recall was a lever, but that was over 50 yrs ago. It was on a flatbed type railroad car, and I think it's still there at the Artillery Museum at Ft.Sill. The barrel was very flexible, for an artillery piece, and was probably 30 ft. long made in what looked like sections. I forget the range but it was well over 100 miles.