Why navies rarely admit a warship failed

Has a navy ever openly admitted that one of its warships was a mistake or failure?

No example is offered; acknowledging a failed design would surrender ground in negotiations with the Treasury.

Calling a warship a mistake would weaken a navy's position with the Treasury. That budgetary concern creates an institutional incentive to avoid a public admission of failure. No specific instance is offered of a navy making such a concession.