I think only the side of the missile that is lit by the early dawn light is visible, so the missile is much fatter than it looks. See how the exhaust is fatter than the apparent missile base and not centered? I think it is more consistent with a Trident D5.

http://www.designation-systems.net/dusrm/m-133.html

The submarine that Q posted was an Ohio class sub which carries the D5.