Why did armies not adopt naval gun calibres to share ammunition already in production?
Short answerNaval guns were generally too heavy to move as practical field artillery, so mobility outweighed ammunition commonality.
NotesThe question compares naval weapons such as destroyer guns with army field artillery. Gun weight and movement are the decisive constraints. A warship can carry a much heavier weapon and its supporting equipment on the hull, while an army must move artillery over land throughout a campaign. Shared calibre or shell production therefore does not erase the mobility penalty of adopting a naval weapon ashore.