Yimmy, as far as I know we only keep one boat on patrol anyway, meaning the other 3 are in the UK which also means that if Britain is struck first then the enemy can destroy these 3. So whether we have 3 boats with 2 in port of 4 boats with 3 in port makes no difference. We will never have all of our SSBNs in port at any one time so in the event there base is hit we will always have at least one. Look at it this way, Britain will only use it's nuclear weapons in a few scenarios. A) If Britain is under major threat of attack in which case we could very quickly get a second boat out to sea in addition to the one already on patrol. B) Britain is hit first, in which case we have a single boat with which to retaliate but considering we only have a single SSBN operating at any one time any then this will be no different to now. C) Britain goes nuts and wants to launch first, in which case we would have ample time to get all 3 boats out to sea. In any case having a fourth SSBN makes little to no difference. In terms of deterent, I still believe that it's the risk to the government's control over the target country that is the incentive for them not to attack you. 64-128 120kt warheads is enough to do enough damage for that in my opinion. Not to mention that any nuclear attack by anyone on anyone else has a major chance of starting world war 3. Nukes are political weapons and should be considered as such in my opinion.

"B) Britain is hit first, in which case we have a single boat with which to retaliate but considering we only have a single SSBN operating at any one time any then this will be no different to now." But you are still mising my point. If we only had three boats, and one were to be destroyed by an unknown, be the sub simply dissapear one day in the middile of the Atlantic or an IED blows it up, we would only have two boats. Two boats is not enough to ensure we have one at sea. Then 2 years later at a time when we do not have one of our two boats at sea we could be attacked with no deterrant of retaliation.

We can keep one at sea with 2 boats for long enough to buy a replacement, depending on availability rates. However it is very unlikley that we would suffer a catastrophic loss of an SSBN and with the budget being as tight as it is I would rather see the money spent on something that is needed and used. Obviously I'd love 4 SSBNs, in fact I'd love a lot more but they are expensive and the RN is having to cut commitments and something has to give.

Yimmy and RM, I see both your points. But I still believe that we should keep the 4 SSBNs. Yes having 3 boats with 1 out would be no different in a nuclear war to having 4 boats with 1 out. But consider that before a nuclear war there is likely to be a period of 2-7 days at least of mounting tensions. Nobody just wakes up one morning with the idea to start a nuclear war - it would happen for a reason. And when we saw that evidence developing - tactical nuclear weapons usage, NBC/WMD usage, suicide bombings in the mainland, prophesies of mass martyrdom, WHATEVER it may be - I'm sure we could very quickly put another 1 or 2 SSBNs out to sea. And having 3 out there in say 4 days, is way better than having 1. And that extra survivability and extra warheads WILL make a difference. In fact why on earth dont we fill all the tubes with Tridents and fill all the Tridents with warheads now, 100% loadout? RM I know what you're saying but we're in an increasingly uncertain world and a little robustness couldn't hurt us. Better to have an extra SSBN and never need it than to need an extra SSBN and never have it. And as we've gone through the massive cost of building the Vanguard class and running costs are much less considerable than initial costs, we might as well use what we have already paid for, eh?

What, so having an extra 64 warheads that aren't usually on patrol anyway will be a credible threat as opposed to having 64 fewer? I disagree. And if it is that bad then each boat can carry an extra 64 warheads while keeping within the START limits. In my opinion 64 warheads is enough to destory the major infrastructor of any nation and more importantly it is enough to trigger a major nuclear war. The threat only has to be enough to stop any leader wanting to launch an attack against you. For that you need to have a nuclear capability of destroying any forces that are moving against you; the UK easily has that with 3 SSBNs, further more you must be able to harm a country to the point it is not worth starting a war with you. 64 warheads can do that. It may not completley destroy a country (only a few countries though) but it could turn any country into it's own hell hole; destroy it's economy, probably destroy any system of power etc et $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ Normally I agree with your posts. Not this time. Only about half of those 64 warheads will actually hit what they are aimed at. Mirvs were created to increase P/K (I think that is how you use the abbreviation for probability of kill). So now you have around 20 targets that will actually be hit. And 20 may not be enough to deter the chinks. No, the UK needs at least 5 boats filled up with warheads. And no I will not help you pay for them either Mr. Blair.

An ICBM can destroy your subs also after a first salvo (which take 8 minutes for all 16 missiles).Ballistic missile launch detection satellites (DSP) pinpoint the subs and a ICBM/IRBM strike the sea maybe less than 20 minutes after (the boat have moved few miles only and a megatonic(s) bomb will crush it 10 miles away) or a SUBROC or ship equivalents in minutes.Your sub will fire one time only. Nations with this capacity today: US, Russia In few years: France (if satellites are developped as planed) and China. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ I really like this idea. I imagine that you can use an ICBM against surface navies as well?

I guess we'll just have to agree to disagree about whether it's a deterant or not. However I've not heard kill probabilities like that for a Trident MIRV before.

About the question of how many nuclear strikes one would need to be able to perform so as to deter China, I have trouble picturing even that most populous and largest nation on Earth not being deterred by 64 120 kt nukes. We're speaking of 16 targets each struck with 4 disks of about 7 km radius.

Some background on the UK?s Strategic Nuclear Deterrence force? -Trident II D5 SLBM (UGM-133) -Missile Range: 12000km -Thermonuclear MIRV: Mk.4/Mk.5 Type , 12 per D5 missile, (UK limitation to three MIRV?s on patrol in accordance to START treaty obligations) -Warhead: AWE W76 Derivative (approx yield 100+kT) -Deployed on 4 Royal Navy Vanguard Class SSBN?s -START treaty limits 48 warheads per SSBN (equal to original Resolution class deployment levels), theoretical maximum of 192 warheads per Vanguard SSBN. -One crew maintained per SSBN. -One SSBM on patrol at any one time, rest at extended readiness or one in refit. There are current proposals to back-fit the Vanguard class to a swing role, non VLS ?SSGN? in conventional support of land based operations. This is one of the reasons submitted in the 1998 SDR for reducing the SSN force from 12 to 10 units along with the enhanced Land Attack capabilities of the Trafalgar fleet submarine class upgrade and Astute class procurement. MIRV Target error margin: 0.07 NM (120 m). This accuracy coupled with it?s reduced vulnerability to enemy missile defences means it is considered a first strike weapon. With it?s virtually invulnerable delivery platform, the SSBN, enhances this with the effect of a surprise attack with little or no warning prior to impact and the nature of the SSBN means that the Trident D5 also forms the cornerstone of the UK and US? second-strike capability in case of nuclear war. Having one SSBN on patrol still gives the UK a universally viable Nuclear deterrence against any nation even though it?s current deployed scale is reduced by treaty obligations. The one ?surplus? SSBN is necessary in order to maintain an attritional insurance in case of any unforeseen circumstances whether it be engineering or otherwise, given the critical nature of the platform?s role in national security. In terms of best possible use in relative peacetime, I think the duel role proposal to use non-patrol SSBN?s in conventional warfare is a good way to maximise our assets given the reduced tempo in SSBN operations post Cold War and our increasing focus on littoral operations and would offer valuable support to the SSN fleet.

Yes. 4 is even the minimum to keep the deterrent doctrine alive. 6 would be better but Uk (like France) lack the money for it. As said by other if you just want to have a nuclear capability one is enought but a deterrent doctrine with at least one at sea at any time need to take into account maintain time and (sth not already said) "surprise law". Wich mean you can't be sure that a technical problem won't take out one of your sub for "unplanned maitain. You also have to take into account the time you will replace the SSBM at their end live by new model. With some management failure or developpement delay you need to have a bit over capability to face this unplanned problem. With only 3 or two you won't be able to certify that's you can have one at sea anytime. 4 is really the minimum number.