Alternate theory on the D5 missile launch.
Some have suggested the boat may have been a dolphin class, and I think that is worth considering.
Dolphin class are diesel boats, and believe it or not they are quieter than our nuke subs when they (the diesel boats) run on battery power.
If a foreign sub was able to sneak into Puget sound, a dolphin class would be the best bet for stealth.
The only issue is vertical launch capability, which is not something they are supposed to have.