Why advanced warship exports could fund development

Did Britain or the United States prevent their shipyards from exporting advanced warship designs?

Not generally; foreign orders helped pay development costs and sustain the supplying country's shipbuilding base.

Britain and the United States generally did not impose blanket restrictions on private yards exporting advanced warship designs. A foreign customer could finance design work, tooling, and industrial experience that also benefited the builder's home navy. Officials therefore had to weigh secrecy against keeping shipyards active and having someone else absorb development costs. This helps explain why second-tier navies could buy highly capable ships from major naval powers rather than deliberately downgraded products.