The known Vickers image is only one part of the wider archival question. A comment points to Armstrong triple-turret variations for Japan dating as early as 1907, suggesting more than one British firm may have explored the arrangement. Russian records may also preserve evidence because Vickers 14-inch guns were considered for the Borodino or Izmail-class battlecruisers in triple mounts. If those export and foreign-order records survive, they may reveal how far British triple-turret engineering progressed even though the Royal Navy did not adopt it.
Notable Point · 50:00-50:32
Where to look for early triple-turret evidence
Possible Vickers, Armstrong, Russian, and Japanese design records offer routes for testing the historical basis of early triple mounts.