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Working Paper - A MULTI-MEGATON WORLD?

Auteur: 
Franco Cozzani
Date de publication: 
22/7/2011

 

Chers Amis,

Nous avons l'honneur de publier le troisième des quatre articles du physicien Franco COZZANI, Chef du Département de Stratégie et Innovation auprès du Secrétariat de l'initiative EUREKA à la Commission européenne, qui sera suivi d'un dernier article (au titre « Fission, fusion and staging ») que vous aurez l'occasion de lire dans la section « IERI News » du site officiel de l'IERI.

 

We are at a point with nuclear weapons

which is very similar to where we would be,

if multi-megaton bombs had never been developed.

 

Freeman Dyson

 

During one single week in 1962, Mankind came closer to self-inflicted annihilation as never before. At the height of the Cuban missile crisis, the U.S. Strategic Air Command was prepared to deliver almost three thousand strategic nuclear weapons, many of them high-yield thermonuclears, with an estimated combined yield totalling seven thousand megatons. Very conservative estimates at the time foresaw at least 100 hundred million dead in the Soviet Union from such an attack. But these calculations followed the "optimistic" scenario of a one-way war, where the United States would deliver a devastating surgical first blow, reducing every single element of the Soviet military system to a burning heap of radioactive debris. It does not take a rabid anti-nuclear activist, though, to believe that the Soviet Union would have fired in return; in 1984, the World Health Organisation instead calculated that a ten-thousand-megaton nuclear exchange would have resulted in 1.15 billion dead and 1.1 billion injured world-wide. All of this without accounting for the possibility - as foreseen by scientists only later, in the mid 1980's - of triggering the onset of so-called nuclear winter, when the soot from the extensive burning of cities and forests would have reduced dramatically the amount of sunshine falling on the Earth surface for a number of years. The resulting reduction of both heat and light irradiation would have altered entire biological cycles, essential to the very sustenance of key food-chains on our planet: from chlorophyll-based photosynthesis of green plants, to the effectiveness of rain forests as climate regulators, from the direct yield of agricultural food crops to the growth and the survival of plankton in the oceans, at the basis of entire sea food-chains, to the growth of bacteria in the soil, again essential in their role of compost and fertilisers in all cultivated lands. Nuclear winter, which would have likely resulted in the starving of yet more millions in the Northern Hemisphere alone, became very fashionable in those years, at the same time the convincing theory of a large meteoric impacti at the transition between the Cretaceous and the Tertiary periods came to be accepted as the main cause for the sudden extinction of large dinosaurs from our planet some 65 millions years ago.

 

The above scenario has constantly defined for many years, for most people, the enduring nightmare of the nuclear age: utter and total annihilation meted on our civilisation by the use of multi-megaton weapons. The perception of nuclear weaponry in collective memory had in reality been varying to a large degree since the last days of World War II. In a world shocked-shelled by increasing brutality against active combatants and civilian populations alike, the war had introduced a new weapon: strategic firebombing against heavily populated cities. The first atomic bombs dropped on Hiroshima and Nagasaki represented for the vast majority of the U.S. Military Command at first only a new weapon of unprecedented individual destructive power, but they represented a sort of extension of the weapons already being used against cities, not the dawning of a new global age of fear. More than a few members of the Government and the Army actually saw them at first just as larger firebombs, and envisaged their use on strategical and ethical grounds which were not so much different from those underlying the conventional large-scale firebombing of civilian populations. As rather convincingly argued in recent studies of the closing days of World War II in the Pacificii, most historians and laymen alike had traditionally, and somewhat erroneously, credited the first atomic bombs with having "finished the war" all by themselves. Despite the poignancy of every recurrence of the Hiroshima bombing (that of Nagasaki is singularly almost always universally forgotten), the devastation of the two Japanese cities must be seen in the correct historical perspective of the time rather than being taken over in a sort of time warp, in which the very different scale of destructiveness of multi-megaton weapons, developed only almost ten years after the end of the war, casts an utterly eerie light on the timeless tragedy of war. Barring the density of the destruction close to ground zero, indeed unprecedented, the first generation, multi-kiloton weapons used in wrath resulted in a scale of destruction not very different from that of the conventional firebombing campaign raging against Japan in the last months of the war. It is incorrect to assume that nuclear weapons became ipso facto true history-changing instruments as of their introduction, or that everybody in the United States involved in the production, deployment and use of nuclear weapons against Japan actually perceived them as totally qualitatively different weapons since the beginning. The Japanese leaders were shocked into surrender also by the entry into war of Stalin's Russia on August 8, two days after the Hiroshima bombing, and the incredibly rapid destruction of the proud and battle-hardened Japanese Imperial Army divisions stationed in Manchuria at the hand of the lighting-fast advancing Red Army. It is also not very widely known that the conventional firebombing of Japan went on, with continuing high level of devastation of cities, reduced to cinders by thousands tons of incendiary ordnance dropped by hundreds of B-29 bombers, after the Hiroshima bombing and in temporal superposition with the second atomic attack on Nagasaki. Further evidence that the United States military was unsure that Japan would be struck into capitulation by the unprecedented destructive power of only two bombs, is provided by the fact that the United States Army Air Force was assembling another plutonium-implosion bomb at Tinian at the moment news arrived that Japan was suing for unconditional surrender. The "third shot" was being prepared, reportedly, for a nuclear attack on Tokyo. Even the effects of radiation, despite the later evidence of its ghastly consequences at Hiroshima and Nagasaki, took a while to simmer into the general mindset of both government and public attention alike. Living proofs of this are the test campaigns carried out in the early second half of the 1940's, when the effect of ten-kiloton class devices were tested against the combat capability of U.S. Army troops, deployed close to the blasts at the Jackass Flats testing range in Nevada.

 

The destructiveness of nuclear weapons gravitated for a few years after the end of the War at about the yield level reached by the first weapons ever used in wrath: a few tens of kilotons, and it was a while before yields started to climb appreciably. According to most accounts, the first ever nuclear explosion, the Trinity shot near Alamogordo, New Mexico, on July 16, 1945, reached 18.6 kilotons. Using the same plutonium implosion design, the "Fat Boy" bomb which attacked Nagasaki reached a yield of between 21 and 23 kilotons, whereas the "Little Boy" uranium gun design which levelled Hiroshima was slightly less powerful, at about 15 kilotons. Yields hovered at about 20 kilotons for quite a while, until improved design started to increase the efficiency of the weapons, achieving a higher percentage of fissile material actually undergoing fission. A brief analysis of early milestone nuclear tests bears this out rather clearly:

 

  • The Baker shot at Bikini, on 24 July, 1946, was a standard "Fat Man" device, the same type of design of the Nagasaki bomb. Baker was not meant to test a nuclear weapon design; it was meant to test a nuclear weapon effect on a small fleet. It yielded 23 kTiii, about the same yield of the Nagasaki blast.

  • The X-Ray shot at Eniwetok, part of the Operation Sandstone campaign, yielded 37 kT on 14 April 1948, using a plutonium-oralloy composite pit. X-Ray was the highest yield device tested up to that time, and was surpassed by the Yoke shot, on 30 April, which yielded 49 kT. Yoke remained the highest yield design tested by the United States until 1951.

The first Soviet developments achieved very comparable yields - not surprisingly so, one could perhaps add, in view of the rather high level of "inspiration" from American designs which had characterised the early phases of the Soviet nuclear programme. Pervaya Molniya (NATO code "Joe-1"), the first nuclear shot at the Semipalatinsk test range in Kazakhstan, reached 22 kT on August 29, 1949. Vtoraya Molniya (Joe-2) followed on September 24, 1951, with a yield of 38.3 kT. These were tower shots, essentially tests of designs very similar to the Nagasaki Fat Man device. Joe-3, tested on October 18, 1951, was instead a weaponised design: Joe-3 was an air bust - air drop test, which yielded 42 kT. One could very well characterise all of these designs as first generation fission weapons; it is quite remarkable that yields improved by a factor of two over about six years: From the 18.6 kT of the Trinity shot and the 21-23 kT of the Nagasaki blast to the 49 kT reached by Sandstone Yoke.

 

It was only with the dawning of the 1950's, that the nuclear age was about to enter the brave new world of higher-yield weapons.

 

The first development was the increase of the efficiency of fission weapons, made possible by better (computer-assisted) calculations of the pit assembly, which allowed for more multiple-point implosions, resulting in a higher fraction of fissile material undergoing fission. The first plutonium devices imploded a pit with 32 points, resembling the external stitched structure of a football (U.S. readers should read "soccer" ball); designs tested during the Operation Greenhouse campaign showed the advantage of configurations with 60 and then 92 implosion points (also referred to as 92 lenses).

 

The second development was the introduction of thermonuclear reactions, in the form of fission boosted designs. In a fission boosted weapon, deuterium and tritium are added to the fissile material, in small quantities, to generate a strong flurry of fast neutrons, capable of increasing the yield of the plutonium and uranium-235 mixture, but also to fast-fission cheap natural uranium 238iv. During Operation Greenhouse, carried out over April and May of 1951, the "George" shot reached 225 kT. The combinations of the two improvements to the design of fission weapons was impressive enough: in 1952, the King test in the Ivy series achieved 500 kilotons with a boosted oralloy design, the most powerful fission device ever detonated by the United Statesv. But much more was in sight.

 

During the Ivy campaign, of which the "King" shot was the fall-back design to a relatively high yield device in case the more advanced concept for a "true" thermonuclear would have failed, the first staged thermonuclear was tested. On November 1st, 1952, Ivy Mike yielded 10.4 megatons, over two-thirds of which came from fast fission of the uranium 238 tamper in the second stage. The "power of the Sun" did not much matter in Mike going beyond 10 megatons, as only no more than one third of the total yield came from the actual fusion of its pure deuterium mixture. One should bear in mind that, in nuclear weapon design, "thermonuclear" is essentially a very efficient way to fission a larger quantity of cheap fissionable - but not chain reaction sustaining fissile - material, and that the direct energy from actual fusion reactions is typically the minor fraction of a thermonuclear blast, unless the warhead is specifically designed otherwise, to minimise the energy yield from the fast-fission channel in the secondary, essentially to reduce fallout.

 

What lied below and around the Mike test rig did not much care about where the energy of the blast was coming from: the islet of Elugelab utterly vaporised, leaving behind a crater some two hundred feet (about sixty meters) deep and more than one mile across. The relative scope of the destruction that this different class of weapons were capable of bringing on living cities is dramatically exemplified by imagining to superpose a nuclear blast on the New York City skylinevi. Ground-zeroing over the Empire State building at Fifth Avenue and West 34th Street, the fireball and the stem of the mushroom for a Bikini Baker-class fission bomb would extend to a diameter of about 800 yards, not enough to actually touch Central Park or the restaurants at Peer 51, although heat, blast effects and radiation levels would hardly make for a pleasant day anywhere in Manhattan. But the Mike fireball alone would have extended to more than three miles from ground zero, completely obliterating all five New York City boroughs.

 

Only two years after Mike, the much easier to weaponise "dry" design, using different mixtures of lithium deuteride and different primaries, were tested in the Operation Castle campaign series at Bikini in March 1954. The first test of the series, the (sinisterly) famous Bravo shot, ran away to 15 megatons; Castle Romeo yielded 11 megatons, and Castle Yankee, also a run-away, yielded 13.5 megatons, the second most-powerful U.S. test ever. The fireballs for Castle Bravo and Castle Yankee expanded to nearly four miles in diameter, and of course ranges for utter destruction from blast, heat and radiation effects from a single weapon of this yield would extend over ranges of tens of miles in radius, that is, over hundreds of square miles in area.

 

Multi-megaton yields, now available thanks to staging, did not come to all World Powers at once. On August 12, 1953, the Russians, who had not yet figured out the principle of radiation implosion, tested their "Sloika" design, Joe-4, a layered "cake" design conceptually not very different from a heavily and repeatedly boosted fission device. Joe-4 reached 400 kilotons, the same range as the advanced boosted pure fission Ivy King. It was only in 1955, on November 22, that the Soviets could test a “true” staged thermonuclear: RDS-37 was restricted to a yield of 1.6 megaton but its design was capable of 3 megatons.

 

It took equally a while to France and China to grasp the fundamentals behind the staging approach. But eventually staged they went: China's first test of a staged device, on June 17, 1967, yielded 3.3 megatons. On August 24, 1968, France followed up with the Canopus shot, which yielded 2.6 megatons.

 

It is hard to define Joe-4 and Ivy King as kindler, gentler nuclear weapons, with yields about 20 times Nagasaki and 30 times Hiroshima, but things should be judged in perspective against the multi-megaton warheads which followed shortly afterwards. About half a megaton was the maximum that a pure - albeit boosted - fission design could practically attain, and also advanced fission devices like Ivy King and Orange Herald consumed far too much precious fissile material to be seriously fielded by armies in sufficiently high numbers to pose a real threat to the very existence of civilisation on Earth. Let us dwell on this point a bit, for it lies at the core of the present article. As far as the level of destruction on a single city, nothing would have matched the use of an Ivy King-class bomb on any living urban community. But one should realise that the inhabitants of Perth would have not noticed an attack on Minsk any more than the citizens of Atlanta had been affected by the firebombing of Hamburg, Dresden or Tokyo at the end of World War II. And, precisely, there was not enough of a supply of fissile material at the time to build hundreds of such weapons, let alone thousands of them.

 

Nuclear is nuclear, but there is a range, and Mankind was suddenly to cross a threshold. With the development of the so-called H-bomb, the United States at first and the other permanent members of the U.N. Security Councilvii later acquired a class of weapons as singularly distinct in destructive power from fission weapons as these earlier developments had been from conventional weapons.

 

The radiation-imploded approach, with a plutonium boosted implosion primary and a second stage employing "dry" lithium deuteride and fast fission in the secondary, using a natural uranium tamper, opened up the road to multi-megaton yields in practical, aircraft-deliverable designs. Still, the first staged, multi-megaton bombs were quite unwieldy by today's military standards: these first-generation staged thermonuclears (one should not make confusion with first generation nuclear weapons) were the heaviest and largest nuclear weapons ever built and deployed by the United States. The EC-17/Mk-17 and the EC-24/Mk-24 came at about 18.6 metric tonnes and 7.5 metres in length, and could only be carried by the huge, turboprop-propelled B-36 bomber. The Mk-17 was the first multi-megaton bomb widely deployed by the U.S. Air Force: 200 of these were built and deployed between October 1954 and October 1957. It was the quickly weaponised version of Castle Romeo, the lithium-deuteride thermonuclear tested right after Bravo, and had a reported yield of between 11 and 12.5 megatons. An "emergency capability" version, the EC-17, with a yield of 11 megatons, was rushed into service between May and November 1954; 5 bombs were deployed. The Mk-24 bomb was virtually identical to the Mk-17, and practically indistinguishable by its external appearance. With the same weight of 18.6 metric tonnes, it reportedly had a somewhat higher yield of 15 megatons. The Mk-24 was based on the device tested in Castle Yankee, which used a different primary in its design. Over 100 Mk-24 were fielded by the U.S. Air Force between October 1954 and October 1956, again preceded by the emergency capability EC-24 version, with a yield of 13.5 megatons, 10 units of which were fielded. Nuclear disarmament advocates and historians alike will likely gasp in horror at the frame of mind which evidently prevailed in the Pentagon in those days. The "emergency capability" EC-17 and EC-24 bombs were rushed into service between April/May and October 1954, in quantities of 5 and 10, respectively, because the U.S. military could not wait five or six months before deploying the series-versions Mk-17 and Mk-24!

 

From their part, the Soviets ran a few years later what is the highest individual yields campaign in the history of nuclear weapon development. Between 1961 and 1962, the Soviets tested warheads yielding slightly more that 19, 21 and 24 megatons, respectively, at their testing range in Novaja Zemlya. On October 30, 1961, the Soviet Union also famously tested the truck-sized "Tsar Bomba" at over 50 megatons, a design capable of yielding some 100-plus megatons when including a uranium tamper for fast-fission in its last stageviii.

 

It is debatable whether Tsar Bomba could have been termed a deployable weapon, albeit some sources maintain that the Soviet Air Force did eventually deploy a few such units for actual delivery by its bombers. The bomb, however, was so large that it needed to be carried outside the bomb bay of a specially adapted Ilyushin; the plane would have likely resulted so unwieldy to manoeuvre, that flying it was possible in a test in peacetime, but hardly conceivable in a real-life military mission over hostile territory.

 

But the game-changing nature of the staging approach was not limited to the thousand-fold increase in yield over the first atomic bombs and the many-fold increase in yield over the most efficient fission designs of later years; it actually laid in the fact that staging achieved its black magic by fast-fissioning large quantity of cheap material. A multi-megaton staged warhead was never meant to murder a single human being more sinisterly that a "normal" atomic bomb or more atrociously than torture in the Middle Ages. Robert Oppenheimer-termed "Plague of Thebes" not only could kill millions rather than "only" tens of thousands with a single air drop, but it could even more immorally kill millions on the cheap, allowing the Armed Forces of the two superpowers of the time to go on an acquisition frenzy and amass too many of them in a very short time span. The "golden era" of the multi-megaton race lasted well into the late 1960's, increasing immensely the destructive potential of the United States arsenal at first, and of both superpowers later, through the acquisition of thousands of weapons. Individual yields did not significantly climb further above that of the first staged designs characteristic of the mid-1950's. Development continued during all of the 1960's and 1970's, essentially improving reliability, deliverability and, to an extent, efficiency. No new radical concepts were introduced and, while specific yields (megaton of blast for ton of weight of the warhead) went up to an extent, the maximum yield of fielded warheads levelled off at about the 20+ megaton level. A notable example was the U.S. B-41 gravity bomb, perhaps the highest specific yield nuclear weapon ever deployed, reportedly having been capable of 25 megatons in its "dirty" version, and thought to have been also a true three-stage device. In 1962, then U.S. Defence Secretary Robert McNamara gave his famous interview to Time, where he claimed that the United States could have deployed, without testing, a 50 to 60 megaton gravity bomb for the B-52 bomber, and a 35 megaton warhead, with testing, for the Titan-II intercontinental missileix, but neither was ever developed.

 

The Soviet Union fitted a single 20 to 24 megaton warhead on its SS-18 ICBM in the 1970's, before shifting to smaller, multiple warheads on its heavier launcher, and it is uncertain whether the Soviet Rocket Force maintained for much longer a few SS-18's armed with a 20+ megaton warhead as a first-strike, nuclear electro-magnetic pulse (EMP) weapon. Some readers might remember how the Soviet nuclear attack on the United States in the blockbuster 1983 television motion picture "The day after" begins precisely with a high altitude EMP blast over a doomed Kansas City. Until when the Soviet forces did maintain this option in their arsenal is debatable, but it is generally concluded that 20+ megaton warheads remained an integral part of the Russian nuclear attack capability well into the mid-1980's.

 

If left with any breath after the concept of "emergency capability" bombs, nuclear disarmament advocates and historians alike will very probably be at a loss at these yield values, perhaps describable as representative of a class of weapons from a doubly foregone era. In the intervening ten to twenty years, military planners shunned the concept of delivering such very high yields on any conceivable military target, in favour of more precise multiple independent re-targetable (MIRV) warheads for land-based intercontinental missiles at first, and sub-marine launched missiles later. Later still, after the end of the Cold War, military planning shifted again from nuclear targeting sovereign nations to developing complex frameworks for conflict prevention, local conflict resolution, and chiefly to fight the spectre of nuclear proliferation among 'unstable" states and, especially, the possibility of nukes in the hands of terrorist organisations world-wide.

 

This evolution in individual yields of deliverable warheads is cast succinctly in the following table. The result is quite graphic.

 

  • Hiroshima bomb (used in conflict, 1945): 15 kT (0.015 MTx);

  • Joe-3, air-deliverable Soviet design (test, later deployed, early 1950's): 42 kT (0.042 MT);

  • Castle Bravo (test, 1954) / Mk-24 (mid-1950's, deployed): 15 MT= one thousands Hiroshima's;

  • B-41 bomb (1960's, deployed) / warhead for the SS-18 Soviet ICBM (single, non-MIRV, 1970's and 1980's, deployed): 24 to 25 MT = over one thousands Nagasaki's, or one thousand-seven hundred Hiroshima's;

  • W-80 warhead for cruise missiles (in service) / W-76 warhead for the Trident II SLBMxi (in service): 100 kT = less than seven Hiroshima's;

  • W-87 warhead for the MX "Peacekeeper" ICBM (in service): 300 kT = twenty Hiroshima's;

  • W-88 warhead for the Trident II SLBM (in service): 475 kT, highest fixed yield warhead currently deployed by the United States = a little over thirty Hiroshima's.

Table 1 Individual yields of milestone tests and actually fielded nuclear weapons.



Presently, most gravity bombs and warheads fielded by the United States do not exceed 100 kT (0.1 MT), and the most powerful compact warheads in both the American and Russian arsenals max out at between 300 to 500 kT (0.3 to 0.5 MT).

 

It is not clear whether the People's Republic of China presently still fields some megaton-class weapons on its inter-continental missiles and the United States ony retired from active service not so long ago its gravity B-53 bombs, capable of 9 megatons, but reportedly maintains some fifty of them in reserve, as back-up option against deeply buried, heavily fortified bunkers filled with deadly bacterial and chemical weapons of mass destruction. However, to most practical effects, multi-megaton weapons are now firmly out of the picture. Still, the cultural paradigm of multi-megaton warheads as the ones uniquely characterising the reality and legacy of nuclear weapons lingers and live on unimpeded. None other than Richard Rhodes, the Pulitzer Prize winner author of "The Making of the Atomic Bomb" and its enthralling, majestic sequel, "Dark Sun, The Making of the Hydrogen Bomb", falls squarely in this category. He wrotexii: "Not Robert Oppenheimer, as he was accused, but physicist and superhawk Edward Teller delayed the development of the hydrogen bomb; but for Teller's obsession with megaton yields, the U.S. could have tested a half-megaton thermonuclear by 1949." On factual grounds, Rhodes is absolutely correct, but some distance must be taken from the intended meaning that multi-megaton weapons were something to be eventually reached by Mankind and never be left behind us afterwards, a sort of a sinister promised land for nuclear scientists and the military establishment alike. For we as a species are no longer actually fielding those multi-megaton weapons! We have witnessed instead a sharp reduction in both the average and the maximum yield of practically all nuclear weapons in the arsenals of the largest nuclear powers. From an historical perspective, one could perhaps observe a sort of system stability at play as far as the destructiveness of individual nuclear weapons is concerned, much as in a physical system that can be in a state of stable equilibrium against perturbations. The multi-year dash to develop and field multi-megaton weapons could be seen as having been such a perturbation. Technically speaking, multi-megaton yields were and are perfectly feasible, but from a military point of view, they became completely useless the moment higher targeting precision and realistic penetrator technologies against deeply armoured underground bunkers became available. In this respect, Dyson is right and Rhodes is not: had Edward Teller not have succeeded in influencing the development of nuclear weapons the way he did, the United States would have indeed fielded (much) lower yield weapons sooner, but the end result - after more than fifty years - did not change. At the level of single warheads, we live at most in a few hundred kilotons world, not in a multi-megaton one. We seem to have hit a plateau in nuclear weapons yield which is remarkably similar to Rhodes' implied "kindler and gentler" yield level, and, while many undoubtedly will dream of Mankind actually getting rid of all nuclear weapons, there are at present no indication whatsoever that the highest yield of normally deployed warheads will climb anywhere above half a megaton any time again in the future.

 

Thinking about nuclear weapons yields is admittedly quite akin to discussing national debt in comparison to a family budget: just as it is hard to fathom the practical difference between the millions, the billions and the few trillions of dollars and euros, so it might be awkward to ponder about the essential difference between the kilotons, the fraction of a megaton and the multi-megaton yields of deployed warheads. Still, even within the esoteric and somewhat sinister discipline of nuclear warhead design, there can be no denying that modern nuclear weapons have become much less destructive on an individual basis. Of course, these weapons remain unprecedented in the level of havoc they are capable to bring upon their targets, when compared with even the most powerful conventional explosives: a 100 kiloton-class warhead, delivering a yield in the range of that carried by a modern cruise missile, delivers a nuclear punch about seven times that of the Hiroshima bomb, and a submarine-carried W-88 warhead reaches the yield of about thirty Hiroshima's. But, as ominous as these values are, we are quite far from the yields and the corresponding levels of destructiveness of a 1960's class device. Let us recall that the fast-weaponised versions of the lithium-deuteride devices tested at Bikini in the mid 1950's, the massive Mk-17 and Mk-24 carried by the B-36 bomber, were capable of delivering a blast about one thousand times the Hiroshima bomb; the later, higher efficiency B-41 reportedly reached a yield of about 1,700 Hiroshima's, about the same as the largest single warhead carried by the Soviet SS-18 intercontinental missile during the 1970's and early 1980's. It is perhaps instructive to stress this point, lest the clarity of the argument be lost: these are not levels from a catastrophic major nuclear exchange; these were yields from a single bomb or warhead! One can easily perceive a clear trajectory in the individual destructiveness of nuclear weapons over their history.

 

The multi-megaton devices which characterised the arsenals of the largest superpowers in the late 1950's to 1970's obviously set the collective view of society about nuclear weapons, whereas in reality the yield of fielded nuclear weapons went up very steeply in the first ten years of their development, hit a plateau for about a quarter of a century, and then decreased very significantly ever since. Today's warheads, even the most powerful ones actively deployed, no longer carry anywhere near that destructive power. A single nuclear blast will no longer devastate a large portion of a country. A single medium-yield explosion will not light up an entire archipelago to the extent Castle Bravo did and its radioactive cloud will not mushroom twenty miles up in the atmosphere, spreading huge amounts of deadly radioactive isotopes well beyond the cruising altitude of modern jet airplanes. In step with the decades-long trend in the labour market in most of the Western countries, also nuclear weapons nowadays have downsized. The doomsday tellers got it wrong; our civilisation was not stopped in its tracks by the insane development of multi-megaton weapons, which were not used in the end. We evolved past them; Dr Strangelove's dreams and our own nightmares hovered over the world for two or three decades in a sort of virtual quantum state, but this state never materialised until it actually vanished. We can take some comfort at the thought that we might be still living in a nuclear weapons world, but that world is a kindler and gentler one after all.

 

Or is it?

 

An Ohio-class submarine in service with the U.S. Navy carry 24 Trident II SLBM's, each technically capable of carrying ten W-88 warheads, although SALT 2 treaty limitations already reduced its in-service payload to eight warheads. The W-88 warhead has a design maximum yield of 475 kT (with an oralloy tamper/fast-fission in its second stage), the highest fixed yield of any actively fielded U.S. weaponxiii. The W-88 warhead exists also in a lower yield version, at 300 kT, likely omitting the oralloy in the tamper of its secondary. Finally, the Trident II SLBM can also carry the older W-76 warhead which has a yield of 100 kT: typically, although the detailed warhead type and count on-board each vessel is classified, and likely to change from one cruise to the other, an Ohio-class submarine is armed with a variety of warheads, both W-88 and W-76, with individual yields as "low" as 100 kT and as high as 475 kT. As a result, one cannot estimate precisely the actual total destructive capability of a U.S. Navy Ohio-class submarine clearing the docks of its base in Norfolk, but it is instructive, and relevant to the considerations exposed in this paper, to calculate nevertheless what its maximum theoretical deliverable payloads would be. Assuming only highest-yield W-88 warheads as payloads for its missiles, the technically feasible payload for the full complement of missiles would reach a total yield of 24 x 10 x 0.475 = 114 MT; for a SALT 2-limited complement of warheads, still with a maximum-yield W-88 warheads, eight per missile, the total value would be 24 x 8 x 0.475 = 91.2 MT. A back-of-the-envelope estimate for a variable mix of W-76's, lower yield W-88's and maximum yield W-88's, eight warheads per missile, would suggest a total destructive capability per boat of some 50 to 60 megaton.

The individual total deliverable yield of a single Trident II SLBM, on the other hand, can be as low as 8 x 0.100 = 0.8 MT and as high as 8 x 0.475 = 3.8 MT for the "SALT 2" payload, while each missile is technically capable of delivering a maximum of 10 x 0.475 = 4.75 MT of payload on target.

 

To put these values in proper perspective, let us recall that the entire total yield of every bomb and artillery shell exploded in World War II has been estimated at about 3 MT, of which the entire conventional firebombing campaign on Japan, from March to August 1945, contributed some 150 kT, or 0.15 MT, including all conventional blast and incendiary explosive dropped over all targets.

 

Let us consider Table 1 again, this time adding these values. The following numbers are indeed quite interesting.

  • Hiroshima bomb (used in conflict, 1945): 15 kT (0.015 MT);

  • Joe-3, air-deliverable Soviet design (test, later deployed, early 1950's): 42 kT (0.042 MT);

  • Entire conventional firebombing campaign on Japan in WWII: 150 kT (0.15 MT) = ten Hiroshima's;

  • Entire estimated yield of all bombs dropped and shells exploded over the entire WWII:3 MT;

  • Castle Bravo (test, 1954) / Mk 24 (mid-1950's, deployed): 15 MT= one thousands Hiroshima's;

  • B-41 bomb (1960's, deployed) / warhead for the SS-18 Soviet ICBM (single, non-MIRV, 1970's and 1980's, deployed): 24 to 25 MT = over one thousands Nagasaki's, or one thousand-seven hundred Hiroshima's;

  • W-80 warhead for cruise missiles (in service) / W-76 warhead for the Trident II SLBM (in service): 100 kT = less than seven Hiroshima's;

  • W87 warhead for the MX "Peacekeeper" ICBM (in service): 300 kT = twenty Hiroshima's;

  • W-88 warhead for the Trident II SLBM (in service): 475 kT, highest fixed yield warhead currently deployed by the United States = a little over thirty Hiroshima's;

  • Average total destructive capability of a U.S. Navy Ohio-class submarine, carrying a mixed complement of warheads: 50 to 60 megatons = up to twenty WWII;

  • Maximum "legal" total destructive capability of a U.S. Navy Ohio-class submarine, carrying a full SALT-2 compliant complement of highest-yield W-88 warheads: 92 megatons = thirty WWII;

  • Maximum "technical" total destructive capability of a U.S. Navy Ohio-class submarine, carrying the by-design possible - not SALT-2 compliant - full complement of highest-yield W-88 warheads: 114 megatons = almost forty WWIIxiv.

Table 2 Individual yields of milestone tests and actually fielded nuclear weapons and conventional war destructive capability against that of modern nuclear weapon delivery systems.

 

The perception of nuclear weapons in the public view-frame has sort of crystallised, to a very large extent, around the singular prospect of the use of multi-megaton bombs. Such class of weapons is now, to all practical purposes, out of the picture, and it is high time to consider the real and present danger of nuclear weapons in a less emotional, more correct framework. The concept of any nuclear explosion as some kind of Armageddon, ending the world as we know it irrespective of yield levels, has led to the fairly simplistic demonisation of nuclear weapons in wide strata of the public opinion and the media, resulting in a somewhat strange situation. On the one hand, the spectre of a global nuclear showdown has dissolved away with the end of the Cold War. For many intellectuals, politicians, opinion-forming individuals, such a prospect is, to all practical extent, gone. As a consequence, the continuing presence of a strong nuclear component in the arsenals of many world Powers is recessed to the back of the public debate and is basically out of the political radar, despite its continuing capacity to mete destruction on our countries of an utterly unprecedented scale. On the other hand, the thought of a nuclear device - of whatever kind and yield! - in the hands of so-called "rogue states" and terrorists has acquired a centrality in defence considerations which might perhaps require some repositioning in our mind frameworks and, consequently, policies.

 

The former danger is hardly debated any longer, but might still turn out to be more serious than it is usually thought. The latter gets all the attention, and it might be exaggerated or, at least, it hides the likely consequences of a military confrontation to prevent even the possibility of one such "rogue state" acquiring some kind of nuclear weapon. There is too much anxiety about everything which carries the tag "nuclear" on it, while our societies continue to be far too much condescending about the possibility and very feasibility of war. Robert Oppenheimer never recanted his role in the development of atomic bombs and actually continued to advocate the strategic usefulness of weapons with yields up to a few hundred kilotons, a yield precisely comparable to the most powerful warheads of today, while he shivered at the prospect of the truly multi-megaton bombs he campaigned so much against in his last years, ruining his own influence on the U.S. Government in the process. But he contemplated a nuclear unipolar world at first, and a bipolar one later, where the particular practical deterrent of bombs with yields up to a few hundred kiloton could arguably be an instrument of restraint. That vision was shattered by the different world that the first multi-megaton weapons created as of the mid-1950's, but our historical prospective now shows that multi-megaton yields came, stayed for a while, and eventually went away. This should be reflected in a repositioning of our viewpoints about nuclear explosives, but we should remember that this is a valid perspective only at the level of individual bombs and warheads. We as a species accomplished only half of our homework in evolving safely beyond the invention of nuclear weapons. Mankind still faces far too many tensions on the world scale, and it has not renounced war as a way to settle those tensions. We are indeed at a point with nuclear weapons which is very similar to where we would be, if multi-megaton bombs had never been developed, but the number of deployed nuclear warheads fielded by sovereign States, and their corresponding capability of bringing destruction on nations, still looms uncomfortably large on our future. Even today, with the lower yields of the individually fielded warheads, there would be basically no escape for our civilisation from the consequences of a major nuclear exchange on a large scalexv. A later article in this series will develop a few reflections about the practical feasibility of the much vaunted "zero option" and the well-meaning, and probably equally ill-posed, prospect of a world devoid of nuclear weapons but still fully bent on waging war.

 

The individual yield of modern nuclear weapons is no longer so mind-boggling to scare us all to the point of cancelling them out of our thoughts, to the point of avoiding a proper and more facts-based framework in discussing them. For multi-megaton bombs have come and gone but multi-megaton arsenals have not, while we have not yet succeeded in un-inventing war in what is still, to all practical extents, a very much multi-megaton world.



About the author

Franco Cozzani is an official of the European Commission, temporarily seconded to the Secretariat of the EUREKA Initiative, where he heads the Strategy and Evaluation Department. He is the author of “Mal d’America” and lives in Brussels with his wife Nilla and daughter Linda Margherita.



Disclaimer

The opinions and the statements contained in this paper, either explicit or inferred, are solely the author's and should not be taken to reflect the views, nor involve the responsibility, of any person whose name appears in the present paper, of the European Commission or its Services and of the EUREKA Secretariat.

The distribution and possible publication of this article, as the sole cultural endeavour of the author, has been kindly authorised by the European Commission, according to provisions of Art. 17 of the Statutes of the Officials and other Agents of the European Communities.

 

Copyright 2010, 2011 © Franco Cozzani

 

 

iThe Chicxulub Crater, encompassing both the Yucatan peninsula and the neighbouring Mexican Caribbean Sea, has been later associated with that impact.

iiMichael D. Gordin, “Five days in August: How World War II Became a Nuclear War”, Princeton University Press, 2007.

iiikT: kiloton.

ivFor an elementary discussion of the principles of nuclear weapons design, the reader is referred to the specific article in this series, dealing with fission, fusion and staging.

vThe most powerful boosted fission design ever tested was arguably the British Orange Herald shot, which reached a yield of 700 kT on 31 May 1957. Orange Herald was heavily fusion-boosted, comprising a U-235 primary surrounded by lithium deuteride. Whether it was more akin to a true fission device, albeit heavily boosted, or whether it was conceptually closer to the Soviet “Sloika” thermonuclear design is – to this author's opinion – mostly an issue of semantics. The point is that Orange Herald was not staged, and its yield was about the maximum one could get without staging.

viRichard Rhodes, “Dark Sun: The Making of the Hydrogen Bomb”, Simon & Schuster, New York, 1995, figs 75, 76.

viiThe United States, the Russian Federation, the Republic of France, the United Kingdom and the People's Republic of China.

viiiTsar Bomba was essentially a propaganda blast, a kind of "demonstration" weapon, which did allow then Premier Nikita Khrushchev to boast that the Soviet Union was capable to field 100 megaton bombs at will. Fall-out from nuclear testing in the atmosphere was already a highly debated political topic in the early 1960's, and the Tsar Bomba test was one of the "cleanest" test ever, with about 97% of the blast coming from fusion. From these values, it appears that Tsar Bomba was a true three-stage design, with fast fission-suppressed secondary and tertiary stages, utilising an inert tamper, probably made from tungsten.

ixThe Titan II liquid - fuelled heavy ICBM was normally fitted with a 9 megaton warhead, identical in its nuclear component to the B-53 gravity bomb, probably the high megaton yield weapon deployed by the U.S. Air Force in the largest number and over the longest period of time.

xMT: megaton.

xiSubmarine Launched Ballistic Missile.

xiiJacket text to "Dark Sun".

xiiiThe B-61 gravity bomb, a variable yield weapon, can achieve a yield over one megaton when set for maximum yield.

xivGraphic as these values are, one should keep in mind that things are never so simple in real life (or real death, in this case!) Before one attempts an exact comparison of levels of devastation capability, it should be clearly kept in mind that the destructiveness-yield ratio of a bomb follows a roughly inverse square power law which makes very powerful (nuclear or conventional) bombs less destructive than a proportionally larger number of smaller bombs. Four present-day 500 lbs conventional bombs destroy more unprotected targets than a single 2,000 lbs bomb. Similarly, ten nuclear warheads, each with a yield of 100 kilotons fully devastate a larger area than a single one-megaton warhead.

xvIf the consequences of a single lower-yield nuclear explosion are to be seen in perspective, those of a major all-out war would actually be worse than most assume. One often forgets the important point of accessibility of natural resources in “restarting” an almost fully destroyed world civilisation: our societies evolved exploiting raw materials, fossil fuels and biomass for energy production, which were essentially easy to find at first. We only recently moved to scout for materials and energy in more remote and less accessible places: drilling for oil in California was easier than digging it out of Prudhoe Bay. Similarly, it took (easy) energy to build better machines that produce energy in a more advanced way: the photovoltaic panels in Germany and the windmills in Denmark needed to be built - using fossil fuels - before they could produce clean energy. A post- “day after” world might simply lack the energy, machinery and manpower to go looking for materials, food and energy sources in the harder and more remote places they are harvested today. Whether a planetary-scale destruction would be caused by nuclear war or by a natural disaster worth of a science-fiction movie, the outcome for the survivors might likely be much worse that one normally thinks. Our civilisation might never recover.

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