velopments have subsequently given us Atlas CEP's under 3 miles, and there seems to be fairly general agreement that Russian CEP's will go to or below 1 mile by about 1963 (U.S. Congress, 1960). Some military observers (Gettings, 1960) forecast 0.5-mile CEP's in 1965 Russian ICBM systems. This guidance progress actually renders obsolescent as a deterrent the 100 p.s.i. ICBM launchers of the Tucson Titan type even as construction is barely begun, a circumstance which makes this writer wonder why Tucson must accept such dire civil defense hazards in the first place. Thus, the Air Force's Lt. Gen. Bernard Schriever (quoted in April, 1960 Astronautics, p. 11) has noted that "when ICBM accuracy gets down to 1 mile, the 100-p.s.i.-protected missile will be 'pretty much finished.'" To counter this accuracy trend, newer missile systems (e.g., Air Force Minuteman) are reportedly to be hardened to 200 p.s.i. Now if the Tucson hardening stays at 100 p.s.i. the predicted CEP reduction augurs diminished attack megatonnage and consequent mitigation of civil defense hazards (along wih cancellation of much of the deterrence value of the Titans); but if design changes are introduced to boost the hardening to, say, 200 p.s.i. or more, Tucson will face just as severe hazards as will now be summarized on the assumption of 100 p.s.i. hardening.

In table I (p. 503) are shown the results of a series of probability calculations which the writer has made on the basis just outlined. The figures in the body of the table show (rounded to nearest integer) the number of enemy missiles of specified CEP and warhead megatonnage that must be fired against each Tucson site as part of a 95-percent-probability salvo from a nuclear aggressor. Note that with CEP's as high as 5 miles, so absurdly high an attack must be mounted as to rule out nuclear aggression on the simple ground that it would be economically out of reach of a would-be aggressor. Even at 2 miles, the national total remains prohibitively expensive to an attacker. But when, as predicted for perhaps 1963, system CEP's fall to 1 mile, nuclear attack on the U.S. Atlas and Titan missiles becomes economically and militarily possible. With 0.5 mile CEP's, credibility of deterrence vanishes for 100 p.s.i. sites, as noted in General Schriever's quoted remarks.

Our Titan has been reported to have a warhead of 7 MT, the Atlas 4 MT, Minuteman and Polaris about 1 MT; Russia is believed to have an 8 MT warhead. It seems plausible to assume that an attack on the Titans might involve 5 to 10 MT warheads, whence table 1 shows that, in both cases, 20 MT would be the total per site. For, say, 300 such sites when the nationwide Atlas-Titan program is completed, a 6,000 MT attack could neutralize that part of our retaliatory machinery. Since our own nuclear stockpile has been reported as about 30,000 MT, we cannot regard such a level of attack as at all out of the question. By operational date of the Titans other superior retaliatory weapons may be in existence, raising to considerably higher levels the total requirements for successful attack on our country; but this will not alter the arithmetic of attack on the Tucson area, since as long as the Titans are operational here they will constitute a highest priority targets that an enemy must seek to obliterate in the first crucial minutes of world war III. That being our concern here, we can ignore the larger strategic questions influencing prospects for such a war, and proceed on the assumption that, if attacked in the foreseeable future, the Tucson Titans would draw 18 times 20 MT, or an areal total of 360 MT. All World War II aerial bombardment campaigns carried out by all combatant forces in all theaters of war totaled about 3 MT (5 megatons of total bomb weight, of which only about half was TNT as distinguished from casing steel); warmaking has undergone a quantum jump.

A corollary implication must be stressed. In the course of extensive but unsuccessful local effort to secure public hearings in which technical objections to the planned Titan deployment pattern might be answered by qualified Air Force weapons experts, many Tucson citizens and at least one Air Force official have intimated that a plea for entirely downwind siting was a quibble in view of the likelihood that stray enemy missiles would land on all sides of Tucson regardless of which side of the community these targets lay at time of any future attack. Now, given the CEP of a weapons system, it is easy to compute the fraction of all inbound missiles that must be expected to land with radial errors greater than any specified amount, and table 2 summarizes a set of such calculations for three CEP's. Note that even with a 2-mile CEP only 1 percent of a large salvo will err by more than 5 miles, while with a 1-mile CEP, the probability of error greater than 5 miles has fallen to one in 10 million. The straymissile objection to a downwind siting plea is categorically ruled out by the kind

of CEP's that are now available, let alone with the kind that will be characteristic in 1964.

It should be made clear to the reader that only surface bursts (as contrasted with air bursts) need be considered here. To attain the very high blast overpressures required for successful attack on hardened sites it is necessary to employ surface detonation, for shock reflection by the ground advantageously increases by a factor of two or more the intensity of pressure rise at the shock front (mach effect). A surface burst leads to crater formation and consequent entrainment into the fireball of a large mass of soil and rock (something like a million tons for a 10 MT detonation) which, after vaporizing and recondensing, forms the vehicle for bringing down much of the fission products in a very short time (formation of so-called local fallout). By contrast, an attack on DavisMonthan Air Force Base or any other unhardened SAC retaliatory bomber base might be best accomplished through use of air bursts, since overpressures of only 3 p.s.i. suffice to render parked aircraft unflyable and since it is a quirk of the relevant shock-hydrodynamical laws that such low overpressures are produced out to greater radial distances in air bursts than in surface bursts. A 1-MT optimum air burst delivers 3 p.s.i. to more than 5 miles, while a 1 MT surface burst delivers the same pressure only to 3 miles. Hence, in view of recent guidance breakthroughs, Davis-Monthan alone might have brought only 1 or 2 megatons to the Tucson area by 1964 if still a bomber base by then (B-47 phaseout by about 1962 makes even this target value unlikely).

Even if Davis-Monthan remained, say, a 5-MT surface burst target beyond 1964, the Titans will remain overwhelmingly the chief civil defense hazard to Tucsonans-in contrast to Air Force press assurances that the Titans would not represent any additional hazard to Tucson.

While comparing surface versus airbursts, one other serious piece of misinformation given Tucsonans demands clarification. In an important television talk made by a local Air Force spokesman during the height of protests against upwind siting, it was suggested that all of the emphasis on fallout dangers was rather overdone inasmuch as no Japanese at Hiroshima or Nagasaki were killed by fallout. This true but wholly irrelevant statement was based on the fact that the Japanese 20-KT attacks were both airbursts. (It seems by no means out of place in this discussion for the writer to assert that these and a number of other quite misleading statements and contrived half-truths or outright distortions marked a great deal of the Air Force's response to the efforts to bring out into the light of public discussion the civil defense hazards implicit in the Titan deployment here. The interplay between science, the public, and governmental or military authorities in the instance of the 1960 efforts to alter the siting plans at Tucson are a dismaying history in the view of this writer. In particular, that history shows the urgent need for far better public understanding of effects of nuclear weapons and of civil defense problems.)

Finally, the above targeting analysis permits preliminary comment on the important question of whether attack on the Titans would wipe out Tucson as a result of blast effects. Typical houses do not collapse until about 5 p.s.i. is exceeded, and only window breakage and comparatively minor structural damage occurs beyond 1 p.s.i.

From joint study of figures 1 and 2 and consideration of the stray missile results cited above, one sees that negligible blast destruction in Tucson will result from attack on the Titans. Similarly, thermal radiation effects will be of only marginal concern in Tucson itself. This confirms as essentially correct an Air Force statement to the effect that the deployment would involve "relatively minor additional blast, thermal, and prompt radiation effects on the base and on Tucson." However, omission of any mention of the tremendous increase in fallout hazards rendered this true statement a most objectionably deceptive one to lay before a trusting but technically uninformed citizen. The identical phraseology was used in Air Force reassurances in other ICBM-base cities.

INTERACTION EFFECTS

All nuclear test explosions and all published data derived therefrom known to the writer involve effects of detonation of single weapons, but Tucson's forthcoming civil defense hazards will be dependent upon physical processes set in motion by detonation of, say, thirty-six 10-MT weapons or seventy-two 5-MT weapons within a 50-mile radius of the city (fig. 1). Here and throughout the following, the single case of thirty-six 10-MT weapons will be considered.

Within what time spread must an attacker program his salvo to arrive on our country? Clearly, all must arrive within the shortest reaction time of all our retaliatory devices. The Titan II which is to be used in Tucson will feature storable liquid propellant and all-inertial guidance, permitting it to be fired from within the launch tube itself without either fuel-up or elevator delays. Reportedly, these features reduce its alert-to-firing reaction time to about 1 minute. It is easy to see that this requires that the enemy's attack programing confine all arrival times, not only here in Tucson but in all other Titan II and Atlas F launch areas (e.g., Wichita, Little Rock, Rome-Utica, Salina, Lincoln, Altus, Roswell, Abilene, and Plattsburgh) to within no more than a minute. A slightly more leisurely pace could be used in attacking Titan I and Atlas D or E launch areas, where the salvo might be spread over several minutes if tactically desirable since these sites will have appreciably longer reaction times. Contrary to some citizens' notions, Tucson's evident vulnerability to attack from ballistic missile submarines lying off southern California in no way alters the above programing requirements faced by an enemy. Hence we must ask how the nearly simultaneous detonation of 36 multimegaton weapons near Tucson may affect civil defense hazards.

First, many bizarre mach interactions are certain to occur where adjacent shock waves intersect. A glance at figure 1 shows, however, that most of the loci of shock collisions will occur in uninhabited desert, so the resultant overpressure increases are of little civil defense concern. That they will occur over a few small communities such as Benson or Marana is not really of any additional interest, since Titans have been located so near these and a number of other small towns as to insure complete blast destruction accompanied by fireball ignition of all combustible materials; mach effects only yield overkill there. (Construction of conventional shelters in these and other small communities near the Titan sites seems wholly futile, yet to the writer's knowledge neither Air Force nor civil defense officials have yet given the citizens concerned any hint of this.) But a second type of interaction, that involving the stratospheric mushroom clouds formed by the explosions, is of very great civil defense interest, in the writer's opinion. The Rand studies (Kellogg, Rapp, and Greenfield, 1957) indicate that an isolated 10-MT detonation produces a mushroom cloud extending from about 55 to 105 kft (kilofeet, or thousands of feet). After stabilization (10 to 15 minutes) its radius is approximately 25 miles, the contaminated portion having a radius of about 17 miles. If, as a first approximation, we plot circles of contaminated radius 17 miles concentric with each Titan site, we obtain the schematic overlap pattern of figure 3 (p. 537). On the average there then exists about a threefold overlap at points within the heavily shaded envelope. Does this mean that the density of fission products will average about three times that for an isolated 10-MT cloud (or, more accurately, six times, since each site is assumed to be hit with two weapons)? No; and this for the following reasons.

The fission products are intermixed with the air pumped into the cloud through the stem and distributed radially by the vortical circulations in the cloud's interior (Kellogg et al., 1957). The total mass of air injected into the stratosphere over Tucson by 36 explosions will be very nearly 36 times that injected by 1 explosion, and this huge mass of air can only be accommodated by vertical or horizontal expansion of the composite mushroom cloud. The great static stability of the base of the ozonosphere precludes appreciable vertical penetration beyond altitudes reached by an isolated 10-MT mushroom cloud. In addition, the mere fact that the pressure is so low there means that only a slight mass increment can be accommodated even by an appreciable rise of cloud-top altitude. For example, the pressure thickness of the 55-105 kft layer occupied by an isolated 10-MT cloud is about 85 mb while that of the next 50 kft is only about 7 mb. Hence even a doubling of cloud thickness could accommodate a mere 7/85 or 8 percent mass increment per unit horizontal area of cloud, yet a doubling of thickness seems statically quite out of question. It appears that we may completely ignore thickness changes, whence we compute a composite cloud radius of about 150 miles, of which about 100 miles will be radioactively contaminated in the case of our hypothesized 360-MT attack (square-root scaling will hold). If an isolated cloud spreads out above the tropopause to 25 miles in about 10 minutes, the above expansion might be accomplished in a time of about an hour, although the writer does not yet see any firm basis for making any precise estimate of this rate, and there are a number of other interesting hydrodynamic questions posed by this conception of the composite cloud that cannot be considered here. We shall see that the great horizontal expansion just described markedly influences Tucson fallout hazards.

DISTURBED AIRFLOW EFFECTS

The important question which this section will seek to answer is another question peculiar to the ultra-high megatonnage the ICBM-base cities such as Tucson will face. Will the enormous total release of energy so derange the local airflow that the latter will be essentially unrelated to pre-attack synoptic conditions? This proves to be an extremely interesting question from the viewpoint of both physics and meteorology, but the very novelty of the problem precludes a really firm negative or affirmative answer at this time. Until quite recently it has been the writer's conviction, as it has been that of others such as Machta (U.S. Congress, 1959, p. 127), that a negative answer was to be given. However, having made some progress in understanding several important details of the energy conversion process, the writer now leans toward the view that during the first crucial hour or two after attack, fallout may be significantly affected by thermally induced convergent circulations in the lower troposphere. Since the energy equivalent of 1 megaton (of TNT) is 4.2 X 1022 ergs, the total attack energy is here 1.3×1025 ergs (equal to almost 1 percent of the kinetic energy of the entire global circulation). Of this total, about 50 percent goes into blast energy, about 35 percent into fireball radiation, 10 percent into residual nuclear radiation of fallout, and 5 percent into the initial nuclear radiation emitted during the first minute of the fireball's life (U.S. Department of Defense, 1957). Of the last two components, we may ignore the residual nuclear radiation energy as being released too slowly to be of any meteorological concern (though of the greatest human concern since it constitutes by far the greatest killing agent of nuclear attack), but the 5 percent of initial nuclear radiation may be considered to be degraded almost immediately to heat.

In an analysis which cannot be detailed here but will be published elsewhere, the writer has examined the rate of conversion of blast energy into heat through the mechanism of nonisentropic shock-wave dissipation processes. The result was to establish that substantially all of the blast energy goes over into thermal energy by the time the shock front has propagated out to where its peak overpressures have fallen to below 1 psi. Figure 2 show that the latter limit is reached at radial distances of 15-20 miles from ground zero for weapons of the yield required for attack on the Tucson sites. The shock heating is so related to peak overpressure as to yield a pattern of quasi-hemisphere isothermal surfaces centered on the 36 impact points, with the degree of heating decreasing radially outward from ground zero. To indicate magnitudes, it may be noted that a 10-MT detonation will produce residual shock heating of about 80° C at 2 miles out from ground zero, while at 4 miles radius the heating is still over 8° C. The residual heating does not fall below 1° C until one goes out about 9 miles from ground zero. The isothermal surfaces of constant degree of heating will not be truly hemispherical because of effects of the decrease of barometric pressure with altitude, but this detail will be ignored here.

Turning to the disposition of the 35 percent of weapon energy that goes into thermal radiation, we note that the composite absorption half-length for all wavelengths and stages of emission is put at about 10 miles in air of 10-mile visibility and 10 gm/m3 absolute humidity (U.S. Department of Defense, 1957), so under typical Arizona conditions, we must expect absorption half-lengths substantially greater than 10 miles. Inasmuch as our concern in this section is with the total conversion to heat energy within some rather large cylinder concentric with Tucson and of radius of the order of at least 50-60 miles, it seems quite conservative and accurate enough for present purposes, to treat the effective mean optical path length lying interior to our cylinder of interest as equal to about one absorption half-length, giving one-half absorption of the 35 percent of weapon energy emitted as thermal radiation.

In all, then, we have perhaps 0.50+0.17+0.05=0.72, or about 70 percent of the total weapon energy, or 9x10" ergs, converted into heat within a minute or two after the enemy salvo arrives.

An inevitable secondary energy source of possible meteorological importance will be the scattered fires ignited by fireball radiations (cf. McDonald, 1959). Using the ignition threshold of coarse grasses and similar vegetation (15-20 cal/cm3 for a multimegaton fireball) we find that each 10 MT fireball will ignite the surrounding vegetation out to about 10 miles from ground zero. Botanical data suggest that grass and shrub cover over the desert floors in southern Arizona will not exceed about 500 lb/acre dry weight which, calculated as cellulose, gives a release of heat of combustion at the rate of about 8X108 erg/ cm3. Substantial portions of the Catalina Mountain forests will burst into

73266-61-35

flame from the fireballs at site 18, those of the Santa Ritas will be ignited by sites 6 and 7, and at least the southern flanks of the Rincons by sites 4 and 5, with the Whetstones, Sierritas, and Tortolitas also ignited but only capable of smaller heat release because of thinner forests. Density of combustible material in the coniferous summits of the first three of these montane forests is perhaps 200,000 lb/acre (some 400 times greater than that of the desert floor). From rough planimetry, the total ignitible high forest area is found to be only about 2 percent of the area comprised by 18 10-mile-radius circles concentric with the Titan sites (double irradiation by two 10 MT bursts at each site does not alter the fact that combustion can yield energy only once), but this still leaves the montane forests as the greater heat source in the ratio of about 0.02 (400)=8. We find about 1.2X102 ergs from desert-floor fires and about 10" ergs from montane forest fires. Comparing with the earlier estimate of direct heating of 9×10 ergs, we see that the fire-heating is only about 10 percent as large. Thus fires cannot greatly add to the all-important initial circulations; but the very fact that the release of the combustion energy will extend over many hours tends to be disadvantageous to Tucson in that it will comprise a persistent even if weak heat source centered roughly on the city (when viewed from the large-scale convergence flows we are here concerned with) and hence aggravates the focussing of fallout effects on the Tucson area.

So far we have found that some 9X1024 ergs of almost immediate heat energy will be put into the area roughly identical with that depicted in figure 1, but not all of this will manifest itself as kinetic energy of organized motion. We next need some estimate of efficiency of this conversion process. It is known to be rather low under normal atmospheric conditions, roughly 1 to 10 percent (Miller, 1951). The writer finds that the classical Margules undercutting analysis (Haurwitz, 1941, p. 251) involves only about a 2-percent efficiency of conversion from initial differences of potential and internal energy into organized kinetic energy. Palmen and Riehl (1957) found about a 3 percent conversion from latent heat into kinetic energy in hurricanes. But reasoning broadly from Carnot's principle (viewing the process as that of a large heat engine), we sense that the abnormally large temperature differences between the heated air and the unheated air surrounding the ring of Titans must inevitably lead to higher Carnot efficiencies than those characteristic of typical meteorological systems. Hence we may take the upper limit suggested by Miller, 10 percent, as a likely value for our present case. This means that 9X1023 ergs of organized kinetic energy may be expected to result from our 360 MT attack. The general nature of the resultant circulations seems clear: There will shortly develop a widespread convergent influx in the lower troposphere, with air moving radially inward from all sides toward the centroid of the heat sources, the city itself.

Will all this represent a discernible derangement of the natural airflow controlled by the preattack synoptic situation over southern Arizona? The question may be rephrased somewhat loosely, but in a form permitting quantitative evaluation, as follows: Will 9X1023 ergs of organized kinetic energy be large or small compared to the preattack kinetic energy in a cylinder centered on Tucson and of radius great enough to represent the block of the atmosphere that will deliver fallout to the city? There are admittedly many uncertainties in even this simpler question. Weighing several factors, the writer feels one must take as the cylinder of concern one whose radius is at least 100 miles. This is not only the final radius of the composite stratospheric contaminated region but is also the order of magnitude of the radius from which influx might be expected to occur within the time of an hour or two at plausible speeds, and is, finally, also the radius from which a mass of air equal to the total mass of mushroom-cloud air could be drawn if the influx were confined to the lowest 10,000 feet of the atmosphere, and the latter seems to the writer to be a reasonable first guess. If, then, we consider a cylinder of 100 mile radius extending from ground to the top of the atmosphere and having the reasonable columnar-mean preattack wind speed of 15 m/sec, we find its total kinetic energy to be about 9X1023 ergs, just the value of the estimated increment of kinetic energy itself. It is, of course, entirely by chance that these two energy estimates have come out identical, but what we seem to have found is that the energy of the induced circulations are neither small nor large compared to the relevant preattack atmospheric kinetic energy.

Hence we can neither ignore these induced convergent circulations nor base all of the Tucson fallout analysis on their effects, a finding that renders quantitative radiological estimates less certain, but which qualitatively implies that