4

DELIVERING THE BOMB

As the Manhattan Project moved closer to developing a working atomic bomb in late 1943, planning for combat deployment of the new weapon began. Despite Einstein’s early thinking that an atomic bomb would be too large to be carried aboard an aircraft, developments in both airplane and atomic technology suggested otherwise by the last months of the year. It was clear that the uranium gun bomb would detonate, and Los Alamos scientists and the military were hopeful that a plutonium gun bomb, codenamed “Thin Man,” would also work. Accordingly, in October 1943, planning for the delivery and combat use of the weapons began at Los Alamos. One of the first tasks, assigned to a grouping of the Ordnance Division led by scientist Norman Ramsay, was finding an aircraft that could be modified to load and drop atomic bombs.

THE B-29

The aircraft selected was a new long-distance, high-altitude heavy bomber, the B-29. The B-29 “Superfortress” bomber was the response of the Boeing Airplane Company of Seattle, Washington, to a US Army Air Corps (USAAC) Data Request in January 1940 for an aircraft that would serve as a strategic weapon, a very heavy bomber. The sleek, four-engine craft, known as Model 345, came off Boeing’s drafting tables as a set of plans delivered to the Army in May 1940. Designated XB-29, the experimental craft then emerged as wind-tunnel models and a full-scale plywood mock-up that impressed the Army sufficiently in May 1941 to order 14 of the model as service test aircraft and 250 production B-29s for combat.

Officially neutral in the rapidly escalating war, the United States was preparing for its inevitable entry into the conflict. In June, as the final design work on the B-29 began in Seattle, President Roosevelt reorganized the Air Corps, merging it with the General Headquarters Air Force to create a more autonomous US Army Air Forces (USAAF), the forerunner of the postwar United States Air Force (USAF). The new USAAF calculated that it would require some 70,000 aircraft for the coming war, and the B-29 was to play a major role as a long-distance heavy bomber. To meet the need for aircraft, the major manufacturers shared the plans for both the B-17 (a four-engine heavy bomber known as the “Flying Fortress”) and B-29 bombers to enable mass production on a hitherto unheard of scale. Boeing’s planes began to emerge not only from their own factory, but also from the Glenn L. Martin Company, Bell Aircraft, and North American Aviation’s factories in Omaha, Nebraska, Kansas City, Missouri, and Marietta, Georgia, with sub-assemblies manufactured by several sub-contractors throughout the country.

The first aircraft rolled out of a Boeing hangar on September 21, 1942. Despite a tragic accident that wrecked a prototype and killed most of its flight crew and military observers, the B-29 program pressed forward. By September 1944, there were 647 B-29s in the USAAF’s inventory, a number that climbed to 2,242 aircraft by the end of the war the following September. In all, 3,996 B-29s rolled out of Boeing, Bell, and Martin’s factory doors. The basic B-29 was 99ft long, with a 141ft 3in. wingspan. Powered by four Wright Cyclone R-3350 radial engines, each with a maximum war emergency horsepower of 2,340, the B-29 flew with a cruising speed of 230mph and a nominal top speed of up to 365mph. Capable of climbing to 31,850ft, the B-29 had a maximum range of between 4,700 and 5,500 miles depending on its load.

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Shown is in this map are a number of industrial complexes and laboratories that were scattered across the United States. In relative isolation and secrecy, they worked under the control of the top secret Manhattan Project, to develop the atomic bomb. (Artist Info)

The B-29 was built to carry huge payloads of up to 20,000lb of high-explosive and incendiary bombs in tandem, fore, and aft bomb bays. As they rolled out of the factories, the USAAF decided to deploy the aircraft to the Far East and the Pacific, as General Henry H. “Hap” Arnold, the Commanding General of the Air Forces, later explained:

We did not consider Germany a possible target for the B-29s because we figured that by the time they were ready, the intensive bombardment schedule we were planning with our B-17s and B-24s would have destroyed most of the industrial facilities, the communications systems, and other military objectives within Germany and German-controlled Europe. On the other hand, we figured Japan would be free from aerial bombardment until we could get the B-29s into the picture.1

The first B-29 bases outside the United States, therefore, were established in India and then in China, the latter flown in over the Himalayas and built behind enemy lines in the isolated areas still controlled by the Chinese in the spring of 1944. The USAAF’s plan was, from mid-1944 when the full production schedule for the B-29 was up and running, to shift to new airbases in the then Japanese-held Marianas Islands to bring the bombers within range of Japan, especially Tokyo. The United States Navy and Marine Corps were tasked with seizing the Marianas, and the invasion of the islands of Saipan, Guam, and Tinian began in July 1944, part of a concerted push that lasted until December. Once those islands were taken, B-29s based there would begin an aerial onslaught to devastate Japan.

In the midst of the rapid build-up and deployment of the Twentieth Air Force, the new air formation devoted entirely to the B-29s with two separate bomber commands within it, the Twentieth and Twenty-First, the Manhattan Project was eyeing the B-29 as the plane to carry the atomic bomb to war. In October 1943, when Ramsay’s group began their work on selecting an aircraft, the basic dimensions of the bombs Los Alamos planned to build were known – the Thin Man would be 17ft long and have a diameter of 23in., and a plutonium core weapon, the Fat Man, would be approximately 9ft long and 59in. in diameter.2 Only two bombers could handle their size and weight: the B-29 or the British Avro Lancaster, but the Lancaster’s bomb bay was determined not to be large enough. It was suggested that “Hap” Arnold had demanded that if an American-built atomic bomb went into combat, an American-built bomber would carry it. Ironically, British-built hardware ultimately carried the atomic bomb in B-29 bomb bays.

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The destruction wrought by firebombing is evident in this aerial view of Osaka, which was leveled by an incendiary raid on March 13, 1945. Robert Haney, an American prisoner of war who survived the attack, described the city as a 25-square-mile “smoldering desert.” (Library of Congress)

By November, Ramsay, working with engineer Sheldon Dike, had selected the B-29. On December 1, 1943, the USAAF ordered Materiel Command at Wright Army Air Field to begin modification of a B-29 that would be flying in from Smoky Hill Army Air Field in Kansas the following day. The directive was titled “Silver Plated Project.” In time, it would be shortened into the codename “Silverplate,” and the 65 B-29s modified for atomic missions would be known as the Silverplate B-29s. Once modified at Wright to conform to prototype bomb shapes also being shipped to Materiel Command, the first Silverplate B-29 would proceed to Muroc Army Air Field in California for testing. To modify the plane to carry a Thin Man prototype, Materiel Command removed a fuselage structural section between the two 12ft-long bomb bays to make a single, 33ft-long bomb bay with a double set of doors. New suspension and release mechanisms for Thin Man and Fat Man bombs were installed, and after more than 6,000 hours of labor, the new Silverplate, itself codenamed “Pullman,” flew to California at the end of February 1944.

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The Manhattan Project needed a special version of the B-29 to create its atomic strike force. Known as the “Silverplate” bombers, the atomic B-29s were a stripped down, faster version with specialized bomb bay doors. Shown here in profile are the two aircraft that dropped atomic bombs in combat, B29-45-MO 44-86292, “Enola Gay,” of the 393rd/BS/509th CG, as deployed from North Field, Tinian, August 6, 1945, and B-29-35-MO 44-27297, “Bockscar,” of the 393rd BS/509th CG, as deployed from North Field, Tinian, August 9, 1945. Original art by Jim Laurier. (Osprey Publishing)

The first tests began on March 6, and ended on March 16 when a Thin Man bomb released prematurely while the doors were still closed. The crew managed to land the plane safely, and after repairs the plane returned to testing in June. The drops of Thin Man prototypes soon ended, however, with the abandonment of the plutonium gun weapon by Los Alamos, and testing shifted to the Fat Man prototype and to the now nearly completed design for the uranium gun bomb, Little Boy. At 10ft in length and 28in. in diameter, Little Boy was a shorter weapon than the Thin Man. It weighed 9,700lb. The Fat Man, as Los Alamos continued to consider its ultimate configuration, would not change radically in size, but the engineers determined that it would weigh approximately 5 tons, or 10,000lb.

Because the Little Boy and Fat Man bombs could fit into the two-bay configuration of a regular B-29, the aircraft was again modified, with the forward bay set to carry the atomic bomb and the rear bay in the standard B-29 configuration for conventional bombs. The twin, modified glider tow cable attach-and-release mechanisms installed in the plane’s first atomic modification, which had failed to work properly in the first tests because the bombs were too heavy, were switched to more reliable British-manufactured Type F release and single-point Type G attachments that did not have the problems of delayed and premature release that had plagued the initial Silverplate mechanisms. With these changes, the Pullman B-29 was returned to the field for further testing in September.

PAUL W. TIBBETS

The Silverplate bombers that followed the first prototype were ordered directly from the Glenn L. Martin Company with the modifications suggested by the Pullman bomber’s experience. One of the major issues with all B-29s was engine trouble, and problems with the Pullman’s engines had delayed its departure for Muroc. An initial group of 17 aircraft, designated as Project 98146-S, was modified at the Martin plant in Omaha after the order was placed in late August. The first three of the second-phase Silverplate B-29s were ready by October, and were flown to the newly established base for training the newly selected atomic crews.

The commanding officer of the atomic strike force was a carefully selected veteran of the air war in Europe and North Africa, 29-year-old Paul W. Tibbets. Born in Illinois but raised in Iowa and Florida, Tibbets had flown in his first aircraft in 1927 at age 12. Joining the USAAC in 1937, the self-assured, outspoken Tibbets was a superb flier who had risen to the rank of lieutenant colonel through his bravery and command abilities. After a conflict with a superior officer with connections had blocked Tibbets’ battlefield promotion to full colonel, Tibbets returned to the United States in February 1943, sent out of the way by friends in high places who knew that Tibbets’ abilities as a troubleshooter were needed to move the B-29 project along. Despite the superiority of the aircraft, problems were rife, and the second prototype had just crashed, killing most of the crew. The “big bomber project was a shambles,” Tibbets later said.3

After a brief stint in Washington, DC, Tibbets was assigned to a new Boeing plant in Wichita, Kansas, to sort out some of the problems. From there, he received new orders to head to Grand Island, Nebraska, to train aircrews in how to fly the B-29. From there he went to Alamogordo for advanced operational training with B-29s. Tibbets had done an excellent job, and the USAAF was pleased with his work, but he was not happy. Following an exciting combat career in Europe and North Africa, Tibbets unequivocally viewed his new assignment in the United States an “emotional letdown.”4 That would change with a summons from General Uzal G. Ent, the commanding officer of the Second Air Force. Tibbets received orders to report to Ent in Colorado Springs.

Arriving at Ent’s office on September 1, 1944, Tibbets was first greeted by Lieutenant Colonel John Lansdale, the Army officer assigned to head up security for the Manhattan Project. After a brief conversation in which Lansdale tested Tibbets’ honesty by asking him about a youthful encounter with the police, a story Tibbets thought no one knew, but nonetheless confessed to, a satisfied Lansdale took Tibbets into Ent’s office. “Deak” Parsons and Norman Ramsay were waiting with the general. Lansdale reported that he was “well satisfied” with Tibbets, and with that Ent told Tibbets he was to be given command of a new, secret combat force that would deliver a “new-type of explosive so powerful that its full potential was still unknown.”5 Ramsay and Parsons then briefed Tibbets on the Manhattan Project and what Tibbets was being asked to do. One problem was specifically developing a method for getting the B-29 to a safe point 8 miles away from the detonation of a bomb. Tibbets calculated that at best a plane would be only 6 miles away after dropping a bomb, but he was confident he could find a solution.

To do his job, the USAAF was assigning an initial force of 15 planes and, in time, more aircraft and 1,768 men. A base, “the farther from civilization the better,” would also be provided.6 Three isolated airfields were available; Tibbets would inspect them and choose one. He would also pick his crews, starting with an available unit, the 393rd Bomb Squadron, then in training at Harvard, Nebraska. The 393rd met with Tibbets’ approval, and after inspection he chose Wendover Field in northwestern Utah as his base. Isolated in the middle of salt flats, and with the closest town a small community of a hundred people, Wendover had been a P-47 training base that was in the process of being phased out. Tibbets wasted no time. He established his office on the base on September 8, a week after his meeting with Ent, Parsons, and Ramsay, and only three days later the planes and crews of the 393rd arrived.

From Wendover, backed by the power of the Manhattan Project, Tibbets reached out to select officers and crews “whose superior skills I recognized.” Martin delivered the first batch of 17 modified Silverplates in October and November. In time, the force at Wendover grew as 28 more aircraft with additional modifications were delivered and a detachment of 51 scientists and technicians from Los Alamos also joined the 393rd. They were there to participate in the Los Alamos drop test program and to take the bomb into combat with the airmen. In early 1945, as the Trinity test loomed on the horizon and Little Boy was in final preparation, construction crews built weapons assembly and handling facilities and bomb loading pits at Wendover.

On December 17, 1944, Tibbets received orders activating his new command as the 509th Composite Group, a unique self-contained “individual air force” that incorporated all of the support elements it required to fly, maintain, and equip itself. The 509th’s organizational structure was:

•  Headquarters, 509th Composite Group, the command element.

•  393rd Bombardment (Very Heavy) Squadron, the combat arm of the 509th.

•  320th Troop Carrier Squadron, the air transportation arm of the 509th, flying personnel and equipment in C-46, C-47, and C-54 aircraft.

•  390th Air Service Group, which included the Headquarters and Base Services Squadron, the 603rd Air Engineering Squadron, and the 1027th Air Materiel Squadron. They oversaw the base’s housing, food, finance, personnel and administration, aircraft maintenance and repair, equipment maintenance and repair, and supply.

•  1395th Military Police Company, a force of 133 men who were responsible for the security of the base, aircraft, and the bombs.

In March 1945, the 1st Ordnance Squadron (Special Aviation) joined the 509th to assemble and handle the atomic bombs. They worked closely with the Los Alamos personnel assigned to the 509th, themselves formally designated the 1st Technical Services Detachment.

With his organizational structure set, aircraft and crews in place, and orders in hand, Tibbets set about molding the 509th into a fighting unit and developing the tactics for atomic attacks using the B-29 over the next four months.

“PUMPKINS” AND TRAINING

The newly modified Silverplates featured two bomb bays, the forward bay for atomic bombs, the aft bay configured for additional fuel tanks. A “weaponeer station” was added to the cockpit for the officer who would monitor the bomb in flight and as it fell and detonated. Another modification, stripping most of the guns and armor off the planes, shed 7,000lb of weight. That would speed up the aircraft and enable it to climb higher, all necessary in Tibbets’ quest to outrace the bomb’s blast. The original engines of the B-29s were not sufficient, and so they were switched to fuel-injected Wright R-3350-41 “Duplex-Cyclone” engines with reversible-pitch propellers that enabled the planes to decelerate in the air or when landing, and to taxi backwards. Also added were pneumatic actuators that quickly snapped the bomb bay doors open and shut.

With his planes modified to better perform their intended missions, Tibbets turned to his crews. His two major concerns were accuracy in dropping the bomb, and flying beyond the reach of the blast. Training for accuracy meant dropping test bombs. The goal was to drop a bomb from 30,000ft and hit a 40ft-diameter target – and not to miss it by more than 200ft. The 509th began training with conventional target bombs, but soon switched to the specially designed “dummy” bombs developed by the Los Alamos team to simulate the size and weight of the anticipated Fat Man weapon. Three separate versions of the ellipsoidal Fat Man shape were developed and tested. Welded into shape from 3/8 in steel, the 10,525lb bombs were packed with concrete or plaster (and occasionally high explosives) and were 128in. long and 60in. in diameter. Because of their shape, the dummy bombs were quickly dubbed “pumpkins,” a name they kept throughout and after the war.

Problems with wobbling and accuracy with the first test bombs led to a new design for the tail fin, a box-structure with baffles made of riveted aluminum that restricted airflow and improved the bomb’s ballistics. Intensive training, with more than 200 drops of “pumpkins,” honed the skills of the 509th’s bombardiers. Tibbets also developed a solution and training to deal with the other problem of distance. Given the speed of a B-29, it would take two minutes to fly 8 miles. If a bomb were dropped from 31,000ft, it would fall for 43 seconds before detonating approximately 2,000ft off the ground. The shock wave from the blast, traveling at the speed of sound, or 1,100ft per second, would take another 40 seconds to travel 8 miles. If the B-29 kept flying straight, it would be impossible to travel 8 miles in 83 seconds.

To avoid the effects of the blast, Tibbets developed a maneuver to push his aircraft past the 8-mile range of a detonation. His strategy was to dive and sharply turn the plane once the bomb dropped, facing the aircraft 180 degrees away from the aiming point. The 155-degree turn was a strain on the aircraft as well as a maneuver that required training and skill, but if done properly it would work. If properly executed, the turn would place the plane 6 miles away, with a slant-line distance of 8 miles. The problem solved, the Tibbets maneuver was another intensive aspect of training drilled into the 509th’s pilots.7 Another aspect of training was the challenge of navigating long distances over water and then land, so Tibbets arranged for long-range flights to Cuba’s Batista Field, near Havana, sending five B-29s at a time for ten-day-long missions over the Caribbean, making bombing runs on a number of small islands that allowed the pilots to train in the difficult task of shifting from over-water to over-land flying.8

PROJECT ALBERTA

As the 509th trained, and as the push for a successful implosion weapon continued at Los Alamos, the “homestretch,” as Parsons termed it in a memorandum to Oppenheimer in February 1945, led to the formation of the powerful Cowpuncher Committee and then, in March, Project Alberta, a match to Bainbridge’s Project Trinity. Parsons, as head of Alberta, was tasked with getting the bombs turned into weapons that had the proper ballistics to drop on target. He also had responsibility for developing the best methods for meeting several challenges: detonating the bombs after dropping them from an aircraft; getting the bombs and their components safely delivered to an overseas advance base; assembling them there; loading them into the planes; and before then, testing the non-atomic aspects of the bombs, which included loading “pumpkins” with high explosive and dropping them.

Parsons drew together a team of scientists and technicians as well as military personnel for Project Alberta, with Norman Ramsay as his scientific and technical deputy and naval officer Commander Frederick L. “Dick” Ashworth as his operations officer and military second-in-command. Ashworth, the senior aviator at the Navy’s Dahlgren Proving Ground, was a recent arrival pulled out of Dahlgren in November and assigned to Wendover to replace Ramsay as the direct technical supervisor of the Los Alamos test program with the 509th. Living in Los Alamos, Ashworth commuted via air to Wendover, and soon got to know the 509th and its men as well as the technical aspects of his job.

Parsons and Ramsay quickly organized their bomb assembly needs – prefabricated buildings, heavy equipment, hand tools, etc. into “kits,” or single-item (on a shipping inventory) packages for shipment via rail and naval transports overseas. Everything was done in triplicate for back-up. Parsons, a meticulous planner, also analyzed the potential effect of the bombs to determine the best height for detonation for maximum effect. Hard working and focused, Parsons personally visited the site of a massive explosion that took place on July 17, 1944, when 1,500 tons of high explosives and tons of shells accidentally detonated at Port Chicago, a naval ammunition loading facility on San Francisco Bay. Parsons would later fly as an observer on a B-29 to watch the Trinity test, and made it clear to Groves that he wished to take the bomb into combat himself, to make sure it all worked to plan.

Project Alberta’s planning was necessary to take the bomb to the Pacific along with the 509th, and from a forward base in the Marianas to strike at Japan. Even as Tibbets assembled his planes and pilots and began training, the Marianas fell to American forces. In June 1944, the US Navy and the US Marine Corps hit the Marianas, striking Saipan before invading Guam and Tinian. Saipan fell on July 9 with approximately 29,000 Japanese and 16,500 American casualties. The American presence in the Marianas drew out the Imperial Japanese Navy, and in the resulting battles of the Philippine Sea on June 19–21, the US Navy achieved decisive naval victories that crippled the Japanese fleet. The invasion of Guam, a prewar US base, took place on July 21, and effectively ended on August 8. Tinian, the last of the three major islands in the Marianas, offered fierce resistance, and the Marines landed in the face of heavy fire on July 24. Aided by P-47 aircraft that dropped napalm on the Japanese defenders, but facing fierce combat, the Marines secured Tinian on August 1, although there, as with the other islands, isolated pockets of Japanese held out for the remainder of the war.

With the fall of the Marianas, the Twenty-First Bomber Command built new bases to extend their striking power into the heart of Japan. Previously, the Indian and Chinese based B-29 bombers could only attack Kyushu, Japan’s southernmost island. From the Marianas, the industrial heartland of Japan, as well as the capital, Tokyo, was now in range. The first B-29s to arrive in the Marianas landed at Saipan on October 12, 1944, to escalate the air war. After a photo reconnaissance flight over Tokyo on November 1, the first raid hit Tokyo with limited results due to high winds and the bombers being blown off target.

High-altitude bombing with high-explosive bombs continued to be the Twenty-First’s principal tactic, but the reassignment of a hard-driving, cigar-chomping new commander, Curtis LeMay, would see a shift in tactics. Relieving the Twentieth’s previous commander, Brigadier Haywood Hansell, Jr., on January 20, 1945, LeMay paid close attention to the horrific results of the fire-bombing of Dresden in February. He also weighed the risks to his men and planes against the tremendous sacrifices being made by the US Navy and Marines as they assaulted Iwo Jima in the face of kamikaze attacks and the fierce resistance of the Japanese Army, which lost nearly all of their 20,000 defenders while killing over 6,000 Marines and wounding nearly 22,000 others.

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Starting in late 1944, the US Army Air Forces used the newly developed B-29s to deliver the first large-scale aerial attacks against Japanese cities. Under the command of General Curtis LeMay, the Twenty-First Bomber Command launched high explosive and incendiary raids that laid waste to some 67 Japanese cities, killing more than half a million and leaving some five million Japanese homeless. In this aerial image taken during a B-29 attack, Tokyo burns on the evening of May 26, 1945. (Library of Congress)

LeMay decided that Japanese anti-aircraft fire was not as well organized or effective as air crews were facing over Germany, and that low-altitude flights with planes loaded with incendiary bombs could bring about the Twenty-First’s combat objective of wrecking Japanese industry, and breaking the enemy’s morale by destroying cities. As the fighting continued on Iwo Jima, on March 9 he launched an incendiary attack against Tokyo with 325 planes loaded with newly developed M69 napalm bombs. Arriving over the city in the darkness of the early morning of March 10, the B-29s unleashed a rain of destruction from the air. When the fires burned themselves out, more than a quarter of a million buildings were gone in a 16.8-square-mile area, and some 83,000 to 100,000 Japanese were dead.9 Following the attack on Tokyo, Le May’s planes struck Nagoya, Osaka, and Kobe. By the end of March, 1,505 sorties by the Twenty-First had hit Japan with millions of pounds of incendiaries. It was, LeMay later said, the beginning of the end for the Japanese. It also marked a new emphasis of the war, as noted by a USAAF spokesman, “the entire population of Japan is a proper military target.”10 By the time of the war’s end, over nine million Japanese were homeless, 58 major cities had been devastated, with a loss of more than two million structures, and more than 700,000 had been killed.11

SELECTING A FORWARD BASE AND TARGETS

In April, as the air war intensified, the 509th began preparations to head to the Pacific. The war in Europe was drawing to a close, and despite Tibbets’ initial thought that his force would divide into two wings, it was increasingly clear that the 509th would carry their new weapon only against Japan. That April, Tibbets set orders in motion to shift planes and crews to Tinian to spur the Manhattan Project into action as the race to meet the deadline for the Trinity test continued. Even as the 509th began to pack, major decisions about their ultimate mission began to emerge.

The death of President Roosevelt on April 12 brought Harry Truman into office. Truman was unaware of the atomic bomb, and on the evening of the 12th, as he took office, Secretary of War Henry L. Stimson briefly told the new President, as Truman later recalled, “about an immense project that was underway – a project looking to the development of a new explosive of almost unbelievable destructive power.” Truman learned more from James L. “Jimmy” Byrnes, another Roosevelt confidante, who assured Truman that the “bomb might well put us in a position to dictate our own terms at the end of the war.”12

After a full briefing by Stimson and General Groves on April 25, two days later an initial meeting of a “Target Committee” to determine where the atomic bomb would be dropped in Japan convened in Washington, DC, at the Pentagon. Groves outlined the priority for selecting which cities to bomb with the new weapon:

…the targets chosen should be places the bombing of which would most adversely affect the will of the Japanese people to continue the war. Beyond that, they should be military in nature, consisting either of important headquarters or troop concentrations, or centers of production of military equipment and supplies. To enable us to assess accurately the effects of the bomb, the targets should not have been previously damaged by air raids. It was also desirable that the first target be of such size that the damage would be confined within it, so that we could more definitely determine the power of the bomb.13

The initial list of target cities under consideration included Yokohama, Nagoya, Osaka, Kobe, Hiroshima, Kokura, Fukuoka, Nagasaki, and Sasebo. It was noted, however, that not all of these would be ideal atomic targets, as the Twenty-First Bomber Command, with a mission of “laying waste [to] all the main Japanese cities,” was “systematically bombing out the following cities with the prime purpose in mind of not leaving one stone lying on another: Tokyo, Yokohama, Nagoya, Osaka, Kyoto, Kobe, Yawata & Nagasaki.” Yet “Hiroshima is the largest untouched target not on the 21st Bomber Command priority list. Consideration should be given to this city.”14

The surrender of Germany on May 7 had no effect on the atomic planning – the realization that the Germans did not possess a workable bomb and that the Nazi nuclear effort had stalled, as well as the devastation of Europe, had shifted the emphasis to Japan months earlier. Truman, meanwhile, had approved a larger group, an “Interim Committee” of senior advisors including Vannevar Bush, James B. Conant, Karl Compton, and his soon-to-be-named Secretary of State, Jimmy Byrnes, to advise him on the uses of the bomb. The Interim Committee met for the first time on May 9. One of their first actions was to suggest that a Scientific Panel be formed to advise them. It was suggested that the group be formed with Arthur Compton, Oppenheimer, Ernest Lawrence, and Enrico Fermi as members. That same day, scientist D. M. Dennison, a member of Parsons’ team, completed a report on the general procedures for the atomic bombing of Japan. He stressed a range of six days to conduct operations, careful assessment of the weather, the use of visual bombing rather than radar, and the importance of rehearsal runs. This set the stage for 509th sorties over Japan that became known as the “pumpkin missions.”

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Project Alberta and the 509th facilities on Tinian, where the bombs dropped on Japan were prepared and loaded on to the B-29’s. This depiction is based on maps prepared by Project Alberta veteran Harlow Russ. (Artist Info)

Meanwhile, the Target Committee, now joined by Oppenheimer, Parsons, Richard Tolman, and Norman Ramsay, who served as advisors, met at Los Alamos on May 10–11. Joined by Hans Bethe and Robert Brode for some of the discussions, the group debated a detailed agenda Oppenheimer had assembled, examining how powerful the bomb would be, the best altitude to detonate it, operational considerations, and a list of objectives, including psychological factors in target selection, use against military objectives, and radiological effects. The list of targets had narrowed to Kyoto, Hiroshima, Yokohama, Niigata, and Kokura Arsenal.

The Interim Committee met again on May 14 and 18. The committee’s deliberations did not involve America’s British allies, an action that was part of the increased American emphasis on security. This mindset was also clear in the discussion over sharing the secret with the Soviet Union, ostensible allies – which was rejected. Also discussed was the role of the bomb in a postwar world. As political implications were debated, a group of scientists led by Leó Szilárd lobbied Byrnes unsuccessfully not to begin what would amount, in their estimation, to a nuclear arms race with the Soviet Union, which they felt would soon have a bomb. Meanwhile, the logistical considerations of bombing continued. The Target Committee, now joined by Tibbets, met again on May 28. Spurred by LeMay’s continued success in devastating Japan, the committee narrowed the target list to Hiroshima, Niigata, and Japan’s ancient capital of Kyoto. Secretary Stimson, in the wake of another successful raid on Tokyo, which burned out another 16 square miles, called Groves into his office on May 30 to review the target list. With a fretful Groves standing by, aware that the report had not yet been sent up through the chain of command, Stimson bridled at the recommendation that Kyoto be targeted. Mindful of its historical, architectural, and cultural significance, Stimson took Kyoto off the list.

The following day, the Interim Committee, after considerable deliberation and discussion on the moral implications of the bomb, and whether the United States should warn Japan, overruled Stimson’s concerns over the destruction of entire cities at Byrne’s urging. With Stimson out of the meeting, Byrnes pushed for a “final decision on the question of the use of the weapon” that he would take to the President.15 That decision was, as Byrnes recommended:

…and the committee agreed, that the Secretary of War should be advised that, while recognizing that the final selection of the target was essentially a military decision, the present view of the committee was that the bomb should be used against Japan as soon as possible; that it be used on a war plant surrounded by workers’ homes, and that it be used without prior warning.16

Regardless of the fact that only Little Boy was available as a workable weapon, and the Trinity test was six weeks away, the United States had by then embarked on an unswerving course to use the bomb, and a precedent had been established in which the bomb’s deployment was a political process, not a military one. Byrnes, formally invested as Secretary of State on July 3, would take that approach with him to Potsdam as Truman’s closest advisor when the President met with Winston Churchill and Joseph Stalin to set the stage for the last acts of the war and the immediate postwar world. While at Potsdam, the report of the successful Trinity test, when it reached the US delegation, brought both relief and determination; feelings shared by Winston Churchill when Truman privately briefed the Prime Minister. Churchill later noted that while the decision was Truman’s, as the Americans had the weapon, he had approved of its use against Japan, and that in their discussion that day the question of whether or not to use the bomb had never been raised. There was “unanimous, automatic, unquestioned agreement.”17 The final preparations for carrying the bomb into the Pacific for the 509th to drop it on Japan were underway, and within three weeks the first attack was scheduled.

A vaguely worded exchange between Truman and Stalin over the fact that the United States now had a “new weapon of unusual destructive force” and Stalin’s rejoinder that he was glad and hoped that they would “make good use of it against the Japanese,”18 masked the fact that Stalin was aware of the Manhattan Project thanks to Soviet espionage and had ordered a Soviet atomic program. While still at Potsdam, Truman decided to proceed with the atomic bombing, noting in his diary on July 25 that while this was “the most terrible bomb in the history of the world,” it would be used:

between now and August 10th… The target will be a purely military one and we will issue a warning statement asking the Japs to surrender and save lives. I’m sure they will not do that, but we will have given them the chance. It is certainly a good thing for the world that Hitler’s crowd or Stalin’s did not discover this atomic bomb. It seems to be the most terrible thing ever discovered, but it can be made the most useful.19

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Atomic strike routes, to and from Tinian and Japan, August 1945. (Artist Info)

On July 26, as the last components for Little Boy and Fat Man made their way to the Pacific, the Allied leaders issued the Potsdam Declaration, stating the terms for Japan’s surrender. It ended with “We call upon the government of Japan to proclaim now the unconditional surrender of all Japanese armed forces,” warning that “the alternative for Japan is prompt and utter destruction.”20 LeMay’s fire-bombing raids, a planned invasion, Operation Olympic, and the atomic missions of the 509th were all calculated parts of the plan for utter destruction.