There's a VGAS proposal out there that would have fitted one, complete with helical magazine, into a Trident launch tube. Capable of firing from persicope depth, only the muzzle would have been above water.It also could have been installed on the Spruances, retired Ticos, Kidds, even Burkes.The worst aspect of DD-21 (AGS)comes pretty directly from Congressional intervention. The initial Navy plan was to field the Vertical Gun for Advanced Ships, which was basically a launcher for rocket-boosted gliding shells. But Congress demanded a trainable gun instead, without relaxing the range or other requirements. So AGS was born.