The issue of mistaking an SSGN attack with an SSBN attack is non existant. Submarines don't have to surface to attack with cruise missiles so you don't have any idea what type of submarine and considering a Trident missile is far larger + generally pretty different in other areas than a Tomahawk there won't be any issues there and considering that's why TLAM-N was pulled (i.e a nuclear TLAM varient would lead to every TLAM potentially being a nuclear attack.) then the distinction between a D5 and a TLAM must be obvious enough to differentiate themselves in a pinch.
The idea that an enemy could know if the sub launching the strike is an SSGN or SSN is silly.
"If this role is required at all" - well it is, as it stands the only vessels that the RN has right now to perform long range surprise surgical strikes is it's SSN fleet and it's been quite valuable and provides a very handy capability and considering the current gen USN SSGNs can carry 7 TLAM per Trident tube (to show the scale of the difference of size) that's a pretty impressive amount of firepower - 154 VL TLAM to be precise excluding any potential submarine launched stocks they may or may not decide to carry.
Astute class subs have the equivalent of the Virginias I think, a mix of heavyweight torpedos or cruise missiles that mount up to 38 total and although increasing this would be very helpful it's completely unrelated to the discussion at hand i.e If we've got a spare SSBN ready to go with one already deployed for CASD should it be able to be called into the SSGN rule if the situation called for it?
EDIT: The only REAL way you could tell - i suppose - is looking at the angle the missile leaves the water as a VL TLAM would probably be more well, vertical. But even then the missile can be identified as a TLAM easily enough and won't be labelled a nuclear attack.
I should clarify, i am not saying that a TLAM would be mistaken for a Trident missile once launched (plainly that would be absurd), but rather a potential adversary would not be aware of the type of submarine that either left Faslane, or that it was tailling.
To an extent, my point is political, rahter than military, but i feel it is valid because the deployment (and ultimate use) of strategic nuclear weapons are a political, rather than tactical weapon.
The UK (current) policy on nukes is one of strategic ambivalance. There will always be one SSBN on patrol 24/7/365. However, there are 3 additional boats one of which is ready to set sail at short notice. No-one outside the core personel knows what it will take to trigger that second submarine from being launched, but they know that if it is launched the UK means business. They also know, that all Vanguard class subs are SSBNs. No uncertainty.
If we were to convert a sub to an SSGN configuration, there would be no obvious way of telling whether the UK decided to send a tactical weapons sysem or a strategic weapons system out to sea.
In the current situation with Syria, where the western powers are on one side, and Russia stands on the other, a suspicious enemy could legitimatly question whether, in a military action, the UK would be sending an SSBN or an SSGN - it would depend on the action planned.
I do think there is a role for a vessel in the RN which can launch significant numbers of TLAM missiles, i just dont think it should be an SSGN. It should be a T45 or T26, with the SSN being able to undertake the role in more dangerous waters.
Hopefully that explains my thoughts further - if there are any points/questions then feel free - i will try to respond when i can.
All the best. Andrew
