The act ended through its own program rather than a simple repeal

Was the Naval Defence Act of 1889 ever formally repealed?

No simple later repeal ended it; its construction program was effectively self-ending.

An opening question asks whether the 1889 act was ever formally repealed, noting that the Washington treaty did not pass through Parliament in the same way. No simple later repeal ended it. Its construction program was effectively self-ending. The brief exchange distinguishes the legal life of an act from the completion or supersession of the construction program it authorized.