Why firing a torpedo from a naval gun becomes hazardous

Could a large-caliber naval gun fire a torpedo?

Only in theory; the torpedo would need a protective sabot, safe separation and water entry, and shock-resistant propulsion, making the arrangement dangerously impractical.

A viewer's suggestion that a 21-inch gun could launch torpedoes leads into the practical obstacles. An 18-inch torpedo would need a protective casing or sabot so its propeller and mechanisms survived the gun's discharge. That casing would then have to separate before the weapon entered the water at a usable angle. An electric torpedo would be safer than a volatile liquid-fuel or oxygen system under the shock of loading and firing. The exchange turns an amusing caliber match into a serious lesson about launch loads, water entry, and magazine safety.