Warship sales remained legal under naval treaties

Was it legal to buy or sell a warship with guns larger than twelve inches during the naval-treaty era?

Yes, provided the parties disclosed the sale and published the ship's treaty-relevant details.

The interwar naval treaties did not impose a blanket ban on exporting a coastal-defense ship or other warship with guns larger than twelve inches. A seller had to notify the other parties and publish the relevant particulars. Those disclosures allowed the treaty system to account for the vessel and judge compliance with its limits. The rule shows how arms-control regimes can regulate transparency and national inventories without prohibiting every third-party sale.