UK deterrent with cruise missiles

[uk 75]

The Callaghan Government had already decided on Trident before it lost the 1979 General Election.
David Owen was amongst those who argued that submarines equipped with cruise missiles (Tomahawk SLCM) would provide a cheaper replacement for the RN's four Polaris submarines.
Other threads have explained in detail the reasons why Trident was chosen then and has been chosen again. In this thread I want to look at what we know about a cruise missile RN deterrent.
The RAF might have lobbied for some GLCM Tomahawks to replace its 48 Vulcans. The difficulties faced at Greenham Common later with US systems were amongst reasons why the RN systems would have been prefered.
The advantage of Tomahawk over Trident was that it could be launched from Trafalgar class SSN and so no new (Vanguard Class) boats would need to be designed.
The disadvantage would have been the vulnerability of Tomahawk to dense Soviet air defences.
The 16 missiles on a patroling Polaris boat were still thought sufficient to destroy Moscow but this was expected to be less certain as the GALOSH ABM system was developed further in the 80s and 90s.
I have not seen estimates for the numbers of Tomahawk salvos necessary to destroy Moscow.
It would certainly have needed more than four extra T class submarines.
There were many documents produced from the 70s on advocating SLCM instead of Trident.
This should help inform the thread. I repeat this is about Cruise options not discussing Trident. Trident is covered elsewhere.

 

[Yellow Palace]

I have not seen estimates for the numbers of Tomahawk salvos necessary to destroy Moscow.
It would certainly have needed more than four extra T class submarines.
There were many documents produced from the 70s on advocating SLCM instead of Trident.

This was looked at in the Duff-Mason Report. To cover Target Set 3B - the least demanding requirement - 400 missiles would be required on dedicated cruise missile submarines. With 80 missiles per boat, that meant five boats on station, from a total fleet of eleven.

The result was that a cruise missile force was considerably more expensive, at £12,400 million for 20 years, than the recommended force of five boats with Trident C4 - 'just' £7,880 million for the 20 year period. Four boats with Trident C5 wasn't considered, but sizing them for C5 and carrying C4 would have come to £7,300 million.

In addition to procurement & operating costs, the UK would need to get cruise missile targeting data. The options for doing so were:

1. Obtain access to the US terrain database. It was believed they would be reluctant to provide as much access as the UK would like.
2. Procure defined routes from the US, with some loss of flexibility and independence
3. Establish a UK-only terrain database, which would be very expensive and might not be possible

Given limited range compared to Trident, and a necessity for evasive routing, the boats would also be forced to operate uncomfortably close to the USSR, increasing vulnerability. In short, cruise missiles were inferior to Trident in every way.

A decision to replace Polaris on the RESOLUTION class with cruise missiles on fleet submarines would be, in effect, a decision not to replace Polaris at all. It might, however, be a viable replacement for the Vulcan in the theatre nuclear forces role. That was, after all, what the USN used nuclear Tomahawks for.

Could a UK government have insisted on a seaborne cruise missile deterrent anyway? I'm certain that they could. If it took the form described in the OP, it would be seen as unilateral disarmament. For some persuasions of government, that would be seen as a good thing.

 

[zen]

Establish a UK-only terrain database, which would be very expensive and might not be possible

Possible in light of then efforts on satellites. Which died with Zircon.

In short, cruise missiles were inferior to Trident in every way.

Absolutely.

It's possible this drives a supersonic cruise missile effort. Such was studied.

 

[Scott Kenny]

The primary flaw with this is that TLAM-Ns would take subs from the available attack-sub force. Then you need the boats physically on station enough of the time, see the analysis posted by Yellow Palace.

Also, note that YP's example needs 400 TLAM-Ns, at 80 per boat. That's requiring an SSGN configuration, since the typical SSN carries about 24 weapons in the torpedo room and no sub will go to sea without a few torpedoes onboard.

This wouldn't be a case of stuffing a VLS array into the forward ballast tanks like the Flight 2 Los Angeles class and carrying mostly TLAM-Ns in the torpedo room, as a VLS 688 can carry about 24-30 TLAMs, roughly 1/3 of what each boat would require for proper deterrence availability. It's not even something like the Flight V Virginia-class with 4x VPMs with 28x Tomahawks amidships and 12x more in the forward VPMs, plus maybe 10-20 tomahawks carried in the torpedo room for horizontal launch.

This would be a dedicated ship class roughly the same size as the Resolution or Vanguard classes.

That proposal requires a dedicated class of SSGN submarines which would be unavailable for anything but the deterrence mission.

 

[Yellow Palace]

Also, note that YP's example needs 400 TLAM-Ns, at 80 per boat.

Not my example - the example of the official UK government study into replacing the Polaris system! It's not like this was some brilliant, cheaper, more independent option that people didn't think of at the time. It was studied in reasonable depth, and rejected on the grounds of being more expensive, less effective, and less independent.

The only people seriously proposing cruise missiles to replace the British deterrent are people who think we shouldn't have a deterrent, but know that they can't say so publicly. So it's a two step plan: replace Polaris/Trident with cruise missiles because it's cheaper and more flexible to chuck a couple on fleet submarines, then after a few years decide that the cruise missiles are impractical so get rid of them.

 

[Scott Kenny]

Also, note that YP's example needs 400 TLAM-Ns, at 80 per boat.

Not my example - the example of the official UK government study into replacing the Polaris system!

Granted.

It's not like this was some brilliant, cheaper, more independent option that people didn't think of at the time. It was studied in reasonable depth, and rejected on the grounds of being more expensive, less effective, and less independent.

The only people seriously proposing cruise missiles to replace the British deterrent are people who think we shouldn't have a deterrent, but know that they can't say so publicly. So it's a two step plan: replace Polaris/Trident with cruise missiles because it's cheaper and more flexible to chuck a couple on fleet submarines, then after a few years decide that the cruise missiles are impractical so get rid of them.

I was trying to hammer home just how bad an idea this was.

Can't just replace half your SSNs torpedoes with TLAM-Ns, it takes too many missiles to give equal coverage to Polaris. You also would have to have boats dedicated to the deterrence mission, on the grounds that an SSN is likely to be a very long way from wherever the deterrent patrol area would be, and not able to get to the deterrent area quickly due to that distance. Which makes any boat not in the deterrent patrol area not a deterrent at all.

Though if the RN had gotten TLAM-Ns with American warheads, you might have signed up for SUBROCs while you were at it, and that would have been a significant increase in capabilities.

 

[Yellow Palace]

Can't just replace half your SSNs torpedoes with TLAM-Ns, it takes too many missiles to give equal coverage to Polaris. You also would have to have boats dedicated to the deterrence mission, on the grounds that an SSN is likely to be a very long way from wherever the deterrent patrol area would be, and not able to get to the deterrent area quickly due to that distance. Which makes any boat not in the deterrent patrol area not a deterrent at all.

On a very rough estimate, putting the UK deterrent on SSNs would require committing the entire force to deterrent operations, with their torpedo rooms almost entirely filled with cruise missiles. That is... almost entirely untenable.

Though if the RN had gotten TLAM-Ns with American warheads, you might have signed up for SUBROCs while you were at it, and that would have been a significant increase in capabilities.

There was some RN interest in SUBROC, but the lack of a conventional option ruled it out. Interestingly, British submarines tended to have bigger torpedo rooms than American ones, so it would be easier to fit in some of the more specialised weapons.

I do suspect that a British TLAM-N would have had a British warhead. The proposed British-owned and operated GLCMs to replace the Vulcan (in addition to the Tornado) would have done.

 

[Scott Kenny]

Can't just replace half your SSNs torpedoes with TLAM-Ns, it takes too many missiles to give equal coverage to Polaris. You also would have to have boats dedicated to the deterrence mission, on the grounds that an SSN is likely to be a very long way from wherever the deterrent patrol area would be, and not able to get to the deterrent area quickly due to that distance. Which makes any boat not in the deterrent patrol area not a deterrent at all.

On a very rough estimate, putting the UK deterrent on SSNs would require committing the entire force to deterrent operations, with their torpedo rooms almost entirely filled with cruise missiles. That is... almost entirely untenable.

Certainly doesn't leave the RN with any submarines to do other jobs...

Though if the RN had gotten TLAM-Ns with American warheads, you might have signed up for SUBROCs while you were at it, and that would have been a significant increase in capabilities.

There was some RN interest in SUBROC, but the lack of a conventional option ruled it out.

Yes, the lack of a conventional warhead messes up SUBROC usability even in the USN. ASROC had a Mk46 torpedo option, but SUBROC never did, which never made sense to me.

Interestingly, British submarines tended to have bigger torpedo rooms than American ones, so it would be easier to fit in some of the more specialised weapons.

Past the Skipjack and Permit class, not so much. 24 weapons per boat is what I can find on the subject, give or take 2 fish. The advantage the early US boats had was that the Mk37s were short, a bit over half the length of a Mk48. Same effect as the difference between number of torpedoes and number of mines a sub can carry.

I do suspect that a British TLAM-N would have had a British warhead. The proposed British-owned and operated GLCMs to replace the Vulcan (in addition to the Tornado) would have done.

Interesting, I wasn't expecting that. Though the Brits could certainly have designed a sufficiently-small warhead to fit into a Tomahawk or SUBROC.

 

[Yellow Palace]

Yes, the lack of a conventional warhead messes up SUBROC usability even in the USN. ASROC had a Mk46 torpedo option, but SUBROC never did, which never made sense to me.

I've heard a couple of possible explanations. Most straightforwardly, the extra length (5' or so) of the lightweight torpedo would make the missile too long for a torpedo tube. On top of that, th SUBROC warhead was supposedly an integrated part of the weapons system (IIRC it carried the guidance), so replacing the nuclear warhead with a torpedo would be non-trivial. The other explanation offered is that SUBROC was sufficiently imprecise that the high-yield nuclear depth bomb was needed for a decent pK, so there was no benefit to a conventional version.

 

[Scott Kenny]

Yes, the lack of a conventional warhead messes up SUBROC usability even in the USN. ASROC had a Mk46 torpedo option, but SUBROC never did, which never made sense to me.

I've heard a couple of possible explanations. Most straightforwardly, the extra length (5' or so) of the lightweight torpedo would make the missile too long for a torpedo tube. On top of that, th SUBROC warhead was supposedly an integrated part of the weapons system (IIRC it carried the guidance), so replacing the nuclear warhead with a torpedo would be non-trivial. The other explanation offered is that SUBROC was sufficiently imprecise that the high-yield nuclear depth bomb was needed for a decent pK, so there was no benefit to a conventional version.

The picture on the wikipedia page makes it look like the warhead end is fairly long, on the order of 1/3 the overall length. If that's the case, then a hypothetical Mk46 SUBROC would only be 1-2' longer.

But that definitely depends on where the guidance package is physically.

Though given the huge warhead, I suspect that the real answer is lousy accuracy. A 250kt warhead has a lethal radius against submarines of over 10km!