Washington treaty rules for warships built for export

Did the Washington treaty forbid signatories from building capital ships for other nations?

No; it required disclosure of foreign orders and prevented the builder from taking those ships into its own service.

The rules addressed the fear that an export hull could become a disguised addition to the builder's fleet. A signatory had to provide the other treaty powers with information about the ship under construction. The arrangement still allowed countries without suitable yards to buy abroad. Its practical value depended on peacetime compliance, because wartime emergencies historically led Britain to absorb foreign orders already in its yards.