UK Thermonuclear Warheads.

[Yellow Palace]

This recent piece may be of interest:
https://super-octopus.com/2026/07/12/was-fife-an-american-adaption-of-the-british-flagpole-device/

While there's no definitive proof, the author makes the case that UK thermonuclear secondaries tested in GRAPPLE found their way into US weapons, namely:

• The Fife II secondary (used in the W47Y2 and W56) was probably derived from Flagpole
• The W38 secondary may have been derived from Dickens

No conclusive evidence, but the arguments seem convincing.

Found the Galosh footprint along with another from the same file. Both have since been censored and removed from the National Archives copy in DEFE 25/335 a file concerned only with Chevaline. However no one asked me to return my copy. So here they are, if they upload.

What's especially interesting here is that there are 31 targets shown, implying two submarines worth of Polaris missiles... with one unaccounted for. Was the 32nd missile meant to double up on Moscow? Provide a reserve in case one of the others failed to fire?

We may never know.

 

[NMaude]

While there's no definitive proof, the author makes the case that UK thermonuclear secondaries tested in GRAPPLE found their way into US weapons, namely:

• The Fife II secondary (used in the W47Y2 and W56) was probably derived from Flagpole
• The W38 secondary may have been derived from Dickens

Interesting however my understanding that the Fife secondary used in W-47Y2 was, like the Piccolo secondary used in the W-47Y1, a cylindrical secondary design, as far as I know all British secondaries test-fired in the Grapple series were spherical.

 

[Yellow Palace]

Interesting however my understanding that the Fife secondary used in W-47Y2 was, like the Piccolo secondary used in the W-47Y1, a cylindrical secondary design, as far as I know all British secondaries test-fired in the Grapple series were spherical.

This point is addressed by the author. Hansen's argument that the W56 must have used a cylindrical secondary is that the US wouldn't have used an unproven spherical secondary. But if UK work was accepted as proving it, that argument disappears.

The essential argument is that the GRAPPLE tests sufficiently proved spherical secondaries to the point that the US felt comfortable using them without its own tests.

 

[NMaude]

The essential argument is that the GRAPPLE tests sufficiently proved spherical secondaries to the point that the US felt comfortable using them without its own tests.

LASL had successfully tested a spherical secondary in the 250KT Redwing Huron shot testing the two-stage EGG device (diameter 15.3 inches, length 43.1 inches, weight 793 lb. Used PBX-9401 and PBX-9404 explosives. Matched the predicted yield. Possible XW-50 prototype), this was a year before operation Grapple.​

 

[zen]

LASL had successfully tested a spherical secondary in the 250KT Redwing Huron shot testing the two-stage EGG device (diameter 15.3 inches, length 43.1 inches, weight 793 lb. Used PBX-9401 and PBX-9404 explosives. Matched the predicted yield. Possible XW-50 prototype), this was a year before operation Grapple.​

But is that the basis of US disinterest in thin walled designs?
And their interest in a thick walled design being tested...

Which raises questions...

 

[Download]

LASL had successfully tested a spherical secondary in the 250KT Redwing Huron shot testing the two-stage EGG device (diameter 15.3 inches, length 43.1 inches, weight 793 lb. Used PBX-9401 and PBX-9404 explosives. Matched the predicted yield. Possible XW-50 prototype), this was a year before operation Grapple.​

That's up for debate.

I've gone through Swords to check where Hansen got that from and it's from him inferring meaning to the "L-3" idea in Warhead Politics (page 131).

"L-3s grew out of the structure of incentives and constraints discussed in this dissertation, which helped govern Livermore from its earliest days and structured the two-laboratory system. L-3s combined old and new, just as had the Manticore designs. One important L-3 design feature, for example, was first tested by Los Alamos in 1956. The concept involved a configuration more difficult to model than other Los Alamos designs with the computational power then available. Although it worked, Los Alamos successfully pursued the more conservative approach. Pressure to get workable H-bomb designs into the stockpile encouraged Los Alamos scientists on this path despite the potential advantages of the more daring design. Livermore revived the idea two years later in L-3s, an example of what Livermore director John Foster later described as his laboratory's role in pursuing ideas initially bypassed in the "frantic race to get something
in [the stockpile].

L-3s achieved their high yield-to-weight ratios by using oralloy, or enriched uranium, in a new way. Greater yields in weapons of comparable weights was the outcome. Scientists at both laboratories had long recognized H-bomb yields could be increased by using oralloy, but it was an expensive material. The reluctance of Los Alamos scientists to make more liberal use stemmed from the postwar need to make limited amounts of fissile material go as far as possible. Livermore scientists joined the nuclear weapons development enterprise at a time when materials were becoming more plentiful, and this shaped their outlook."

In a vacuum, sure, the first paragraph could be read as that, but the second paragraph puts that in doubt. Slapping in extra HEU is not something unique to spherical secondaries.

 

[Zoo Tycoon]

This point is addressed by the author. Hansen's argument that the W56 must have used a cylindrical secondary is that the US wouldn't have used an unproven spherical secondary.

The essential argument is that the GRAPPLE tests sufficiently proved spherical secondaries to the point that the US felt comfortable using them without its own tests.

Regarding the Spherical vs Cylindrical secondary. L Arnaud’s book Britain and the H Bomb notes the British chose the Spherical form because they thought it made the calculations easier. Conversely R Rhodes’s book Dark Sun, notes the Americans chose the Cylindrical form because they thought it made the calculations easier.

I’ve seen kind of thing in my professional life, it depends who has the strongest personality in the early project days.

 

[NMaude]

I've gone through Swords to check where Hansen got that from and it's from him inferring meaning to the "L-3" idea in Warhead Politics (page 131).

Which volume is that from?

L-3s achieved their high yield-to-weight ratios by using oralloy, or enriched uranium, in a new way.

Oralloy is weapons-grade U-235 (At least 93.5% U-235 enrichment), anyway my understanding of this new way was for the secondary to have nested concentric cylinders alternating between Li6D and Oralloy with an Oralloy spark plug in the middle. I do believe this was first tested in the 1956 operation Redwing Tewa and Zuni shots testing UCRL's BASSOON and BASSOON PRIME devices three-stage TN designs where the BASSOON PRIME device's tertiary had alternating layers of Li6D and natural Uranium in concentric cylinders, I do believe that this is described in Howard Morland's excellent Holocaust Bomb: A Question of Time essay.

The BASSOON device yield 3.5MT with an 85% fusion yield while the BASSOON PRIME device yielded 5MT with an 87.5% fission yield (It was very dirty), ultimately this led to the ultra-high yield B41 three-stage TN-bomb.
​

L Arnaud’s book Britain and the H Bomb notes the British chose the Spherical form because they thought it made the calculations easier.​

The British had far greater computational constraints than the Americans had during the 1950s, availability of suitable mainframe computers governed the pace of TN-bomb development at Aldermaston.​

 

[Download]

Which volume is that from?

Volume VI, pages 443-444

 

[NMaude]

Volume VI, pages 443-444

Thanks.

 

[NMaude]

In regards to the EGG-device tested in the 1956 Redwing Huron shot it was followed up by the 1958 Hardtack Olive shot:

During the Olive shot of operation HARDTACK Phase I at the PPG on July 23, 019058 , UCRL had fired a 218.7lb, 12.6" diameter, 32" long two-stage device that had a predicted yield of 50 to 125KT; actual yield was 202KT, 162% of the higher prediction. (Reportedly, at about this time, there was a discovery of a "Pivotal technology" at UCRL that constituted a major "... breakthrough (That was)one of the two real fundamental contributions of the Livermore Laboratory" and which was originally applied to the POLARIS warhead)​

Volume VI, page 444.

The Olive shot device used a LASL GNAT primary (The same primary used in the LASL EGG-device two years earlier) and a UCRL designed spherical secondary called the TUBA (Volume VI, page 445).

I have no doubt that the detailed design of this two-stage UCRL test-device (Along with the test results) included int the data-package the British nuclear weaponeers got in 1958 after the successful conclusion of the Operation Grapple test series. This device was likely weaponised at a weight of 250lb and a diameter of 14" and no doubt was the base for the Polaris A3's W-58 warhead.

Edit 1: I suspect that this particular innovation for improving the efficiency and yield of a spherical secondary was alternate layering of concentric shells of Oralloy and 95% Li6D.

Edit 2: It has just occurred to me that it has been 70 years since operation Redwing was conducted.​

 

[NMaude]

A bit off-topic but I noticed after checking that there isn't a thread on this board dealing with the US atmospheric nuclear test programmes so I wonder if the Military forum would be the appropriate one to open such a thread in?

 

[xena]

I think here in this forum should be the right place as munitions. Feel free to open a thread, please. Nukes are interesting.

 

[Zoo Tycoon]

I suspect that this particular innovation for improving the efficiency and yield of a spherical secondary was alternate layering of concentric shells of Oralloy and 95% Li6D.
.​

Every time I’ve read about alternate thin shell layering in the secondary it’s connected with unsatisfactory performance. Wasn’t it in the late fifties there was a fundamental rethink about the interaction between the x-rays and the plasma within the radiation case? I remember reading that one test that deleted the polypropylene spacer with a surprising unexpected under yield…. Hence the role of the plasma wasn’t understood which lead to a fundamental discovery?

 

[NMaude]

Wasn’t it in the late fifties there was a fundamental rethink about the interaction between the x-rays and the plasma within the radiation case?

I don't think that had to do with alternating layers of Oralloy and Li6D but with the outer most layers which controlled the ablation pressure profile (It was this ablatively induced collapsing pressure pulse that compressed the secondary before the initiation of fusion reactions).​

 

[Download]

Edit 1: I suspect that this particular innovation for improving the efficiency and yield of a spherical secondary was alternate layering of concentric shells of Oralloy and 95% Li6D.​

Lorna Arnold in Britain an the H-Bomb strongly suggests that highly layered secondaries are not the key. The layering likely causes R-T mixing of fusion fuel with HEU which dilutes the fusion fuel and reduces burn.

Off the top of my head, in Swords, Hansen gives the fission yield for Hardtack Olive as something like 195kt on 203kt total yield (expected yield was about half that). To get layering with such a high fission yield, the fusion layers would have been paper thin, worsening the R-T problem.

A bit off-topic but I noticed after checking that there isn't a thread on this board dealing with the US atmospheric nuclear test programmes so I wonder if the Military forum would be the appropriate one to open such a thread in?

Might be worth having a general US testing thread, not just atmospheric stuff.

 

[NMaude]

Off the top of my head, in Swords, Hansen gives the fission yield for Hardtack Olive as something like 195kt on 203kt total yield (expected yield was about half that). To get layering with such a high fission yield, the fusion layers would have been paper thin, worsening the R-T problem

Given that the fusion yield was only 8KT I suspect that there was only a single layer of Li6D, if it was a test of a multi-layer secondary then I suspect that the other layers would've used Li7H which is inert in terms of fusion reactions.

Edit: I checked the Nuclear Weapons Archive operation Hardtack I test table and the predicted yield of the Hardtack Olive shot was 50KT to 125KT.

 

[NMaude]

All of the British TN warhead designs tested in the Grapple series of tests have had their total yields declassified but what about their fusion yields? I'd like to know how dirty they were when they were detonated.

 

[zen]

During the 1960s, one of the Polaris options examined by the United Kingdom was for a "mini Poseidon" which would have replaced the Polaris A3's three W58 Mark 2 RVs with six smaller W78 Mark 3 MIRVs used in the Poseidon SLBM. Ultimately, the "mini Poseidon" option was rejected in favor of the Chevaline penetration aids and decoys upgrade for the Royal Navy's Polaris SLBMs.

A "mini Poseidon" would have been a significant firepower upgrade for the Multilateral Force's Polaris-armed ships and submarines.

REFERENCES:

Jones, M. (2017). The Official History of the UK Strategic Nuclear Deterrent: Volume II: The Labour Government and the Polaris Programme, 1964-1970. Taylor & Francis.

Stoddart, K. (2012). Losing an Empire and Finding a Role: Britain, the USA, NATO and Nuclear Weapons, 1964-70. Springer.

 

[Scott Kenny]

A "mini Poseidon" would still be limited range and basically operating more as nuclear cluster bombs than MIRVs. City deleters, not bunker busters.

 

[zen]

City deletion was the main reason for the Deterrent effect.

 

[NMaude]

City deletion was the main reason for the Deterrent effect.

That's what those massive multi-megaton monsters* deployed SAC in the 1950s and early 1960s were for.

*They were the Mk-17/24, Mk-21 and Mk-36 with later on the Mk/B-41 three-stage TN-bomb (Retired in 1976).

 

[Justo Miranda]

A bit off-topic but I noticed after checking that there isn't a thread on this board dealing with the US atmospheric nuclear test programmes so I wonder if the Military forum would be the appropriate one to open such a thread in?

It is a politicizable issue, especially after what happened in Hawaii after the test in low orbit became known. I don't think the issue can prosper.

 

[Scott Kenny]

City deletion was the main reason for the Deterrent effect.

Trident had the accuracy to hit military bunkers.

 

[NMaude]

Trident had the accuracy to hit military bunkers.

IIRC the Trident II has a CEP of ~600ft.

 

[Scott Kenny]

IIRC the Trident II has a CEP of ~600ft.

90m. About 300ft.

STRATCOM commander has stated that he's watched tests where the target point was inside the impact crater.

And in general I don't think you'd want to be within 90m of a 100kt boom. Nevermind if it's a W88 delivering 475kt!

 

[NMaude]

I've opened and posted a new thread on US Atmospheric Nuclear Tests Discussions.

 

[zen]

Trident had the accuracy to hit military bunkers.

Which the UK wasn't that interested in.

 

[FighterJock]

Surprised at that zen.

 

[xena]

Which the UK wasn't that interested in.

In what then? Simply to nuke cities?

 

[zen]

UK didn't think a nuclear war was winnable by the early 60's and the abandonment of concepts of ABM.

From it's projected arsenal of a few hundred weapons, the threat of city busting, or more bluntly mass slaughter was the chief driver of Deterrence.
Since the UK itself was clearly doomed if the attacker uses a similar few hundred weapons.

Mutually Assured Destruction.

Not ideas of fighting a nuclear war to win. That is the privilege of great distance, large states and deep arsenal's.

This is why the UK signals it's SSBN what is effectively 'don't launch' signals.
If the signals stop, open the letter and discover if the PM wanted revenge for his or her death and the death of millions of British Subjects. Who already will be dead at that point and millions more wishing for it.

The tactical weapons provided a means to delay the escalation from the limited conventional stocks of munitions to the exchange of millions of lives. A brief window to step back.