Did modernized Royal Navy capital ships keep their old Mark IV torpedoes?
Short answerNo; they could receive Mark IX torpedoes because the standard 21-inch tubes accepted newer weapons.
NotesModernization did not leave the ships tied to their original First World War torpedoes. The Royal Navy upgraded them to Mark IX weapons. Retaining a standard 21-inch tube made that change possible. Standard calibre therefore preserved an upgrade path even when the surrounding capital ship was much older than its new ammunition.