There have been 192 test firings of the D5, which are drawn from a common pool of missiles, of which 10 are acknowledged as having failed. Several of these have been terminated due to telemetry issues for safety reasons. That’s about a 95% success rate.
I think knowing we have a boat at sea with between 8-12 missiles with a 95%+ success rate counts as a deterrent.
Reference the difference between firing a DASO telemetry round and an operational round, the photo below is of Vanguard with the DASO telemetry mast for a test firing. If there is an issue it’s probably related to either the hardware or software interface between the test equipment, missile, sub and shore flight termination system than the missile itself.
