I think both you and dimtar are confusing SLBMs with cruise missiles. The Trident II has a range of over 4000nm, only half the Minuteman III ICBM's range, with

I think both you and dimtar are confusing SLBMs with cruise missiles. The Trident II has a range of over 4000nm, only half the Minuteman III ICBM's range, with a similar flight profile to the ICBM. SSBNs have a significant advantage in that they are mobile and to some degree hidden. A first strike can target ICBM launch facilities and effectively neutralize them, meaning those birds either fly when the balloon goes up or they don't fly at all. SSBNs have to be hunted down and destroyed individually. This provides a retaliation capability that cannot easily be destroyed by a massive first strike. They are "second strike" in the sense that they will be available to respond to any nuclear attack, no matter how overwhelming, thus ensuring MAD remains an effective deterrent to nuclear weapons use.