Since the gun could only be loaded while the sub was surfaced, it had to sink its target in one shot, which was unlikely to be the case against warships, even something small and unarmored like a destroyer.
Good luck managing to hit a destroyer with a fixed gun.
I would imagine that if you did manage a hit though, it would be devastating. I don’t think there were many ships that could shrug off hits from a 12 inch gun. Even if it didn’t sink, it would probably be badly damaged, which might give the sub the opportunity to surface somewhere safe, reload, and shoot again.
The destroyers at the Battle off Samar took multiple hits from Yamato’s 18.1" guns. The initial hits were armor-piercing rounds that passed right through without doing much of anything, but they took multiple hits before sinking even after the Japanese switched to high-explosive shells. I think a single hit on a destroyer from a 12" shell would certainly not sink it, and depending on where it hit it would probably not even be seriously disabled. Given the close range (less than 1000 yards), the destroyer’s deck guns would still knock out the sub pretty quickly.
Since the gun could only be loaded while the sub was surfaced, it had to sink its target in one shot, which was unlikely to be the case against warships, even something small and unarmored like a destroyer.
https://en.wikipedia.org/wiki/HMS_M1_(1917)
Good luck managing to hit a destroyer with a fixed gun.
I would imagine that if you did manage a hit though, it would be devastating. I don’t think there were many ships that could shrug off hits from a 12 inch gun. Even if it didn’t sink, it would probably be badly damaged, which might give the sub the opportunity to surface somewhere safe, reload, and shoot again.
The destroyers at the Battle off Samar took multiple hits from Yamato’s 18.1" guns. The initial hits were armor-piercing rounds that passed right through without doing much of anything, but they took multiple hits before sinking even after the Japanese switched to high-explosive shells. I think a single hit on a destroyer from a 12" shell would certainly not sink it, and depending on where it hit it would probably not even be seriously disabled. Given the close range (less than 1000 yards), the destroyer’s deck guns would still knock out the sub pretty quickly.