Slight thread drift perhaps but I have amended (in bold) Tourists earlier statement to read :
The Vanguard submarine fleet has never, ever actually found out if it can do what all the sims and exercises make them think they can do. No missile has left a rail in anger. Those that actually do their jobs know that reality and exercises are very different.
Surely it's all about deterrence - be it AD/QRA or big buckets of sunshine. I'd rather have a big stick and not have to use it than try to fight with a small one.