The SSBN's, tasked with being shadows in a hole in the bottom of the deep sea, will only act on orders sent that can be confirmed. A movie got made about that with Denzel Washington.
Cruise missiles of the nuke flavor were removed from all surface ships by Order of one of the President Bush's. A Surface Combatant can still drop kaboom of other flavor in your back pocket from over 500 miles away, a CBU (Cluster Bomb Unit) is outright nasty if you are on the receiving end.
Carrier Groups have an Admiral and each ship has a Captain. WHY would ships accept an Air Force order to fire?
Been a reason the Services have been kept at each other, and not just to give Enlisted somebody to fight to keep them busy.
Examine the "Nuclear Triad" again. Who can actually issue those orders and who can say such orders were confirmed?