If I remember correctly, nuclear deterrence with planes flying 24/7 in the skies was still a thing until the early 2000s. It took a long time for the Air Force to scale down that role.
"Following Operation Desert Storm, the dissolution of the Soviet Union and the de facto end of the Cold War, President George H. W. Bush and Secretary of Defense Dick Cheney directed SAC to take all bomber and refueling aircraft and Minuteman II ICBM's off of continuous nuclear alert on 27 September 1991[85] and placing said aircraft on quick reaction ground alert"
So, still ready for Armageddon, but with a bit higher latency.
And ICBMs, too.
I prefer the idea of submarines, though. There were several cases of very serious incidents involving planes losing control and crashing while carrying nukes, at least with submarines the collateral risk on population is much less.
Water is a very good neutron regulator for fission reactions and general radiation absorbant. Not sure how it deals with fusion though (given that it contains hydrogen and a nuclear blast can probably rip apart water molecules pretty handily).
