Who built Royal Navy gun turrets?

Who made the gun turrets for Royal Navy cruisers: the shipyards or the ordnance companies?

Both. Royal Navy yards could do major turret work, Vickers was a leading manufacturer, and other firms built to Vickers or Admiralty patterns.

Turret work was distributed across naval yards and ordnance companies. Major Royal Navy yards, including Plymouth, possessed useful heavy-engineering capabilities and could undertake important work. Vickers was a leading private manufacturer and an especially powerful force in construction. Other companies also produced equipment to Vickers or Admiralty patterns, allowing standard designs to be distributed across a broader industrial network. Naval armament therefore depended on public yards, prime contractors, and licensed or pattern-based production.