I have searched my own files on nuclear weapons and the USSR, without success. I have checked John Newhouse (War and Peace in the Nuclear Age) and McGeorge Bundy (Danger and Survival). Neither history of the nuclear age (the latter by a Cold War era policy maker whose father was a WWII era policy maker) mentions the Tsar Bomba. My own A Brief History of MAD (for which I did a comprehensive review of the literature) fails to mention it either. [This is only available privately, but can be emailed.] However I did find my materials on hydrogen bombs. What we seem to have is a terminology confusion: you are using "tamper" where the literature uses "sparkplug." But the sparkplug is indeed oralloy - it is set off by x rays - and its heat causes the fusion inside it. If one substituted lead for the oralloy, the stage would fail altogether. And that would certainly not cut yield in half. The story still does not work. One would need many stages to reach 100 mt yield - probably too many for any real bomb casing - the time to set of the last stage would exceed the time before the casing burst - by a factor of 4-8 if my back of the envelope values are close. It would make more sense to just remove the stage - and to approach half yield one would remove about half the stages (probably one less than half). Nevertheless, I had forgotten that the sparkplug is made of oralloy. I also wrote to an army expert in nuclear history and a librarian with military interests. I am going to look for data on the ABM test I think may be the basis for this story. For one thing, the dates are about right. For another, the yield is in the same range, and more than a close order of magnitude greater than the biggest US test. And the Russians wanted to keep secret how their ABMs work - so the story may even have been an attempt to hide that. [They thought a single interceptor could take out a sector for half an hour or so for ALL incoming weapons if the bomb was big enough.]

Andre Sakarov describes this project in his memoirs. The web material is apparently derived from a Russian museum and it uses somewhat different terminology than we would use for the same things. But in fact, the term "tamper" means the outer layer of the initial fission bomb. It is called "tirtiary" because, the Russians reason, the fission core is the "primary" (fission) reaction, the injection of fusion fuel into the core causes the "secondary" (fusion) reation, and the fast neutrons from both of these cause a "tirtiary" reaction in the uranium of the tamper. All materials do indeed say this tamper was replaced with lead. But that was not all they did. They also "tampered" with (pun intended) other stages, until they got a lower yield - because otherwise the bomber would not have escaped! While there was no practical application even in theory, apparently two were made, one for testing and one for "deployment" - which later resided for a time in the Russian Atomic Museum. The test of this device in 1961 is several years sooner than the giant test of the ABM warhead, so it is probably the world's second largest bomb - relegating the US hydrogen bomb test that got out of control to third place. Russia did tend to use 20 megaton warheads on missiles - to compensate for inaccuracies. USAF also carried bombs of that size in bombers for a time. Eventually the Russians went for 2-3 mt warheads and we went for 0.5 to 1 mt. [The figures are not variable because of uncertainty, but because the weapons could be set to different values.]

Spark plug is a completely different thing altogether. You cannot simply replace the spark plug with lead or the fusion stage will not work. Moreover, spark plugs are inside the fusion stage not surrounding it. When I said tamper, I meant tamper not spark plug. There is one place where I did misuse terminology (I did not anticipate that it would result in a debate, so I was liberal in my usage of terms). I originally called the tamper the tertiary. It is, of course, not a tertiary, but because the fission of a tamper (when uranium or thorium is used) does add to the explosion, it does in effect function as a stage and hence I used the term tertiary for it to differentiate it from the normal fusion stage. It was inaccurate and I would not have done so had I known that the design of the Tsar Bomba would become the subject of debate. BTW: Here is a schematic of an Ulam-Teller nuclear device that uses a fission primary and a fusion secondary. Notice that the fusion secondary has both a spark plug AND a tamper: http://nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html#Nfaq4.4.2

Hmm, the Guinness Book of World Records also mentions the Tsar Bomba test as the largest ever explosion (I forget the link, but do a google search on the book and you can find it online). But now that you mention it, way back in 1993 or thereabouts when I was rummaging through a Guinness Book of World Records I have a feeling that I did come accross the largest nuclear explosion being cited as 64 Megatons, though I cannot be certain - it was long ago and I was a young kid at the time. If my memory is correct, however, I wonder why they changed it? Still, if you eventually do manage to find more info on the ABM test you mentioned, I would appreciate if you could share it with me, since it does sound intriguing.

In fact French have the same but I don't know exactly how it works.Also a network to detect nuclear explosion.It seems there is input of status of Russia deployment which if a red line was crossed in west Germany an automatic retaliation by nukes on rear echelon and some key russian facilities would have occured first.Then if some major Frenchtwn were hit, on Russian town according to plans. It was the key for deterrent to "faible au fort": to be independant on president will! The story said that when De Gaulle spoke to Russian about it in the end of 60ies, Brejnev became white!

Scary thought, because if this exists in France, French nuclear weapons must be pre-targeted... but on whom are they targeted these days? Russia only????

With numerical systems you don't need to pretarget, only to have different plans to select then download.Some for Russia, China, and all nuclear powers I guess, selected by imputs of thread analysis.

But I thought the whole point of an automated system was to launch without human input in case of decapitation. Hence, you have to have pre-targetting. You mentioned Russia and China - can French ICBMs reach China though? It is very far - much further than the distance between the USSR and the US.

The French have a handful of M-45 sea launched ballistic missiles, with a 600kt payload and a maximum range of 5,000 km. In 1996, France eliminated its land-based ballistic missile arsenal. So, sure, they COULD hit China. Assumeing they parked an SSBN of the coast of Japan. Curiously, France is the only Western nation which is actively working to modernize and upgrade its strategic nuclear capability. On targeting, their SSBN's carry pre-loaded target packages on magnetic disks. Theoretically, to re-target their ballistic missiles (assumething the intended new target is included on one of the packaged disks) should take only 3-4 minutes (time enough to upload the data from disk to missile). This is similar to the systems used for SLBM's in the US and UK. Lengthy re-targeting times for land-based ballistic missiles come from the fact that you dont typically keep target packages on hand. The data has to be computed and uploaded manually, taking 20-30 minutes. But, if your caught at see with the wrong disks, you cant shoot. Thats the disadvantage..

M45 have 6500 km range and 6*120 kt MIRV .We can shot on China from north of soviet union.