British aircraft nukes again?

[Scott Kenny]

No one other than USSR tried it, and there this capability was forced by constant threat to boomers. It's a capability you have to specifically design into the boat (space launches themselves are violent events, and you're offloading big chunk of submarine's displacement in a short order).
Chances that such full salvo will either (1)force interruption, or (2)damage the boat even without even enemy interference (potentially making part of its load temporarily or permanently useless) are quite high.

Also, for smaller nuclear powers, launching full salvo of your only SSBN on patrol leaves your country effectively at a mercy of an opponent(even if it's already a fighting zombie).
In case of extended deterrence, mercy is also extended to those relying on it.

Full salvo as a concept is somewhat viable when you can expect to have >1 boomer in position (or in dispersal bases).
In this case yes, imminent and unavoidable threat to single unit, upon judgement of commander, may force full salvo.

Realistically, full salvos are almost universally impractical for UK and France. Even at a cost of potential immediate counterforce on the boomer itself, and despite full assumption that second tier nuclear power's C&C will not make it.

Wrong. The Tridents were designed to be capable of a full salvo. We flopped the hatches every return from patrol in the launch hydraulic lineup, to move the grease around and make sure everything still moved. It only takes a few minutes, with the full sequence delays built into the system. Unlock hatch, flop open, pause to allow missile to leave, flop shut, lock hatch. 5 steps in process, and at least 2 hatches were in each step at a time.

If a full launch could damage the ship, so could a single launch. So the ships are designed for a full salvo.

The hovering and missile compensation systems need to be able to handle a single missile every however often. The time between launches in a full salvo is enough for the systems to finish the process. It works the same way for one missile as for all of them. IIRC D5s are heavier than their volume of seawater, so Missile Comp has to bring on more water as additional ballast. While C4s were lighter than a tube full of water, so MC had to push water out. Big pumps, moving thousands of pounds of water per second. Pipes were set going through a valve so that water was already moving and you could move 1 valve 90deg from "idle" to pump water out or bring it in. Hovering tanks are at the aft end of the missile compartment, Missile comp tanks are at both ends to better balance the load changes as birds left.

Also, with 4 boats and 2 crews each, the UK should have 3 Tridents out at sea 24/7. (same applies to the French, but different sub name)

Scenarios where it's reasonable are truly rogue/mad ones, and are deeply secondary.

While nuclear warfighting is an insane concept, it's a very cold-blooded, calculated insanity.

Yeah, I know. I have a few Strategic Deterrent Patrols under my belt.