Posted elsewhere (in pieces), but I think it needs more development. So I'll ask here as we have people here who might assist.
Good title needed in lew I'll use "benefits of SSNs"
It's a first stab at trying to define what the SSN delivers for a state.
‐-------------------------------------
Like all naval ships, the submarine possess a quality of both tactical utility and strategic effect.
At the tactical level, the ability to remain submerged and not reveal itself, coupled with the ability to deliver ship killing 'effectors' (torpedoes and, land attack and Anti-Ship Missiles, mines and special forces), makes this a potent means to dominate the seas and threaten coastal infrastructure.
It's strategic quality is in part the familier 'in being' readiness for action, and the retention of ambiguity in where it may be.
This ambiguity used to be a quality possessed by all ships beyond the sight of land. Essentially their location becomes conjecture and assumption, since it is not verifiable.
With the increasing passage of time the uncertainty of the ships location increases, until it is sighted again or another ship sees it and brings that information back to land.
Modern sensors render the ship's location much more acquire-able in real time. Removing ambiguity.
But the submarine retains this quality. Sonar is much more limited in range than radar or vision. Where an aircraft can be detected hundreds of miles away, a submarine can slip past the mere tens of miles and sometimes a lot closer.
Infamously, the more daring submarine commander has risked detection to take pictures of an opponents ship's propellers. A feat requiring the submarine to risk actual collision.
'In being' is the state of readiness to move, and act. A standing Army possesses this quality as does in it's readiness, a fortress manned and provisioned. As such these forces exert an immediate and continuing pressure to be answered either by manoeuvre or by counter force.
As such the nuclear powered submarine delivers an effect far greater than it's actual capacity. It's stocks of torpedoes and missiles are limited, there is little extra accommodation for passengers.
But the possibility is that these effectors will be applied at key assets an opponent possesses.
Ship(s) so vital to the fleet, or transport laden with crucial asset(s).
The port you cannot afford to have blocked. Infrastructure you cannot have have damaged or destroyed.
Worse that unguarded part of your coast through which agents delivered by submarine might slip unnoticed into your country.
Because the submarine might be anywhere, your only defence is to be strong everywhere and this drains resources away from other tasks.
It certainly is the case that nuclear power provides effectively limitless range and endurance only constrained by consumables and human factors.
An SSN for example could continuously power along at 25kts for days, weeks, even months.
25kts is 25 nautical miles per hour.
In one day that equates to 600nm
In one week 4,200nm
In one month 16,800nm.
In six months 100,800nm
And at no point does it need to surface.
Deployment of them is a clear indication of intent.
Deployment from Home, is ambiguous as to it's destination and consequently ambiguous as to where and why it is deployed.
So again ambiguity is another benefit. It signals something, but this is as much in the mind of one's enemies as any intent one has.
For a distant state with multiple areas of operations and concerns around the world. Sending an SSN out, reveals no real clue as to where it is going.
Every state in an area of operations will take note. But they cannot be sure it is heading towards them or someone else.
Worse, once submerged, unless it's located by some happy accident, you don't know, even after it could have reached you if it's here or somewhere completely different.
Maybe it is out there, ready to sink your ships, strike inland or deposit agents into your territory.....
But maybe it is actually on the other side of the world.
And you may only know which, after it has already done it's dirty deeds.
Or worse, decades after when files are declassified and you realise, they (users of SSNs) never felt the need to bother with you and your various schemes.....and you were jumping at imaginary shadows for nothing.