I saw a piece on the Discovery channel over the weekend about teh amazing 16" HARP gun. I never saw it fired but did see it and the spare barrels, up close and personal, back when I was involved in ordnance testing out on the Yuma Proving Grounds.
https://kjzz.org/content/359404/how-giant-space-gun-ended-middle-arizona-desert
https://kjzz.org/content/359404/how-giant-space-gun-ended-middle-arizona-desert