An unresolved question about the largest US-built Royal Navy vessel

What was the largest Royal Navy vessel built in the United States?

The discussion does not settle it; a frigate or support ship is suggested first, followed by escort carriers and large cargo ships.

The exchange does not settle which Royal Navy vessel built in the United States was the largest. An initial guess points to a frigate or support ship, while later chat suggestions raise escort carriers and cargo ships in roughly the 15,000 to 20,000-ton range. None of those candidates is confirmed before the discussion moves on. Caption damage obscures part of the original question, so assigning the distinction to one ship would overstate the source.