The chief characteristic of the conflagration… was the presence of a fire front, an extended wall of fire moving to leeward, preceded by a mass of preheated, turbid, burning vapors. The pillar was in a much more turbulent state than that of [a] fire storm, and being usually closer to the ground, it produced more flame and heat, and less smoke. The progress and destructive features of the conflagration were consequently much greater than those of [a] fire storm, for the fire continued to spread until it could reach no more material… The 28-mile-per-hour wind, measured a mile from the fire, increased to an estimated 55 miles at the perimeter, and probably more within. An extended fire swept over 15 square miles in 6 hours. Pilots reported that the air was so violent that B- 29s at 6,000 feet were turned completely over, and that the heat was so intense, even at that altitude, that the entire crew had to don oxygen masks. The area of the fire was nearly 100 percent burned; no structure or its contents escaped damage. The fire had spread largely in the direction of the natural wind.
A bombardier who flew through the black turbulence above the conflagration remembers it as “the most terrifying thing I've ever known.”
In the shallower canals of Shitamachi, where people submerged themselves to escape the fire, the water boiled.
The Sumida River stopped the conflagration from sweeping more than 15.8 square miles of the city. The Strategic Bombing Survey estimates that “probably more persons lost their lives by fire at Tokyo in a 6-hour period than at any [equivalent period of] time in the history of man.” The fire storm at Dresden may have killed more people but not in so short a space of time. More than 100,000 men, women and children died in Tokyo on the night of March 9-10, 1945; a million were injured, at least 41,000 seriously; a million in all lost their homes. Two thousand tons of incendiaries delivered that punishment — in the modern notation, two kilotons. But the wind, not the weight of bombs alone, created the conflagration, and therefore the efficiency of the slaughter was in some sense still in part an act of God.
Hap Arnold sent LeMay a triumphant telex: CONGRATULATIONS, THIS MISSION SHOWS YOUR CREWS HAVE GOT THE GUTS FOR ANYTHING. Certainly LeMay did; having gambled and succeeded, he quickly pushed on. His B-29's firebombed Nagoya on March 11; firebombed Osaka by radar on March 13; firebombed Kobe on March 16 — stocks of M69's were running low and M17A1 clusters of 4-pound magnesium thermite bombs, less effective, had to be substituted; firebombed Nagoya again on March 18. “Then,” says LeMay, “we ran out of bombs. Literally.” In ten days and 1,-600 sorties the Twentieth Air Force burned out 32 square miles of the centers of Japan's four largest cities and killed at least 150,000 people and almost certainly tens of thousands more. “I consider that for the first time,” LeMay wrote Norstad privately in April, “strategic air bombardment faces a situation in which its strength is proportionate to the magnitude of its task. I feel that the destruction of Japan's ability to wage war Ues within the capability of this command.” He had found a method, LeMay had begun to believe, whereby the Air Force might end the Pacific war without invasion.
At Oak Ridge guests removed their shoes before entering a house. Hiring was still increasing on the muddy Tennessee reservation and construction continuing, challenges to the meager ground cover that a Tennessee Eastman employee was moved to immortalize anonymously in verse:
Mud measured progress: Ernest Lawrence's calutrons, built at such great expense, had begun enriching uranium. A minimum of 100 grams per day — 3.5 ounces — of 10 percent U235 came through the Alpha racetracks beginning in late September 1944. But poor planning for chemical recovery of that feed from the Beta tanks wasted some 40 percent of it, as Mark Oli-phant reported to James Chadwick from Oak Ridge early in November: “This loss or hold-up… has resulted in a very serious delay in the production of material for the first weapon… The chemistry, viewed as a whole,
I believe to present an appalling example of lack of coordination, of inefficiency, and bad management.”
A copy of Oliphant's complaint went to Groves, who must have acted quickly; the troubleshooting Australian physicist could report to the general two weeks later that “the output from the beta tracks has shown an abrupt and very satisfying upward trend.” In his letter to Chadwick, Oli-phant had noted a Beta output of only 40 grams per day; now “an output of about 90 grams per day [has] been reached and there [is] reason for believing that this level would be maintained, or even increased, during the coming months.” He concluded optimistically that “there is now a definite hope that continued effort on the part of the operating company and others will lead early in the New Year to a plant output of the order of that expected.”
As of January 1945 on any given day about 85 percent of some 864 Alpha calutron tanks operated to produce 258 grams — 9 ounces — of 10 percent enriched product; at the same time 36 Beta tanks converted the accumulated Alpha product to 204 grams — 7.2 ounces — per day of 80 percent enriched U235, sufficient enrichment to make a bomb. James Bryant Conant calculated in his handwritten history notes on January 6 that a kilogram of U235 per day would mean one gun bomb every six weeks. It follows that the gun bomb required about 42 kilograms — 92.6 pounds, about 2.8 critical masses — of U235. Without further improvement the cal-utrons alone could produce that much material in 6.8 months, and Conant noted after conferring with Groves that “it looks as if 40–45 kg… will be obtained by July 1.” Ernest Lawrence's monumental effort had succeeded; every gram of U235 in the one Little Boy that should be ready by mid-1945 would pass at least once through his calutrons.
Conant also contrasted his assumptions of June 1944 with his assumptions at the beginning of the new year to draw up a problematic balance sheet: while he had previously “believed a few bombs might do the trick” of ending the war, at the beginning of 1945 he was “convinced many bombs will now be required (German experience).” The German experience was probably the determined German resistance that was prolonging the war in Europe, particularly the counteroffensive through the Ardennes known as the Battle of the Bulge that had begun in mid-December and still threatened Allied lines at the time of Conant's notes. It was partly Allied frustration with such continuing resistance that would lead in another month to the atrocity of the Dresden bombing.
Houdaille-Hershey was finally delivering satisfactory barrier tubes for the K-25 gaseous-diffusion plant. Union Carbide had scheduled barrier delivery to take advantage of K-25's organization as a cascade; as individual tanks, called converters, arrived, workers hooked them into the system and tested them for leaks in atmospheres of nitrogen and helium with the portable mass spectrometers that Alfred Nier had designed. When a stage was leakproof and otherwise ready it could be operated without further delay, and the first stage of the enormous K-25 cascade was charged with uranium hexafluoride on January 20, 1945. Enrichment by gaseous barrier diffusion in the most advanced automated industrial plant in the world had begun. It would proceed efficiently with only normal maintenance for decades.
The pipes in Philip Abelson's scaled-up thermal-diffusion plant, S-50, leaked so badly they had to be welded,
