I've just completed two campaigns.
In the first the SSBN's where part of a large surface fleet in the Barents sea.
In the second they where well outside the Barents, west of Spitzbergen near the pole; this group consisted of 2 x Alpha's, 2 x Victors, 2 x Delta's and a Tango.
Make sure you engage the SSBN's first or they'll just turn away and put the pedal to the metal and be gone.