The 509th Composite Group, Tinian and the Decision to Use the Bomb

On the northern tip of Tinian, a small island in the Marianas some 1,500 miles south of Tokyo, a fenced compound sat beside the largest airfield in the world in the summer of 1945. Its crews flew B-29s with an arrow or a letter on the tail, practiced dropping single, oddly shaped bombs, and told no one why. On 26 July a heavy cruiser anchored offshore and sent a crate and a canister ashore by landing craft. The same day, in Potsdam, the United States, Britain and China warned Japan of “prompt and utter destruction.” Four days later the cruiser was at the bottom of the Philippine Sea, and the bomb she had carried was being assembled in an air-conditioned building a few hundred yards from the runway.

Why it mattered

The Manhattan Project’s laboratories and factories produced a weapon. They did not, by themselves, produce an attack. Between the autumn of 1944 and the end of July 1945 the Army built a separate organization to carry the bomb to Japan, chose the cities it would be used against, and took the decisions, some of them formal and many of them not, that turned a laboratory device into a military operation. This chapter follows both tracks: the 509th Composite Group, which trained in the Utah desert and flew to war from Tinian, and the committees in Washington, Los Alamos and Chicago whose recommendations reached President Truman at Potsdam.

The two tracks met in late July 1945. The Trinity test had shown on 16 July that the plutonium implosion design worked (Chapter 6); the uranium gun-type bomb, never tested, was judged certain enough to use. A directive signed on 25 July authorized the first attack “after about 3 August 1945.” The Potsdam Declaration followed on 26 July. On the same day, USS Indianapolis delivered the core components of the first bomb to Tinian; four days later she was sunk by a Japanese submarine, with the greatest single loss of life at sea in the history of the U.S. Navy.

How the decision to use the bomb was made, and whether it should have been, has been argued over since 1945. Historians do not agree, and this collection does not pretend that they do. The aim of this chapter is narrower: to set out what the record shows about who decided what, when, and on what information, and to separate that record from some of the stories that have grown up around it. The debate itself is taken up at the end of Chapter 9.

A group built for one mission

Planning for the delivery of an atomic bomb began long before there was a bomb to deliver. By 1943 the Los Alamos laboratory knew that both of its designs, the gun-type uranium weapon and the implosion plutonium weapon, would be far larger than any bomb the Army Air Forces normally carried, and that only the new Boeing B-29 Superfortress had the range and the bomb bay to lift them. Modifications to the aircraft, under the code name Silverplate, began as early as the autumn of 1943, and test drops of dummy bomb shapes were made from a modified B-29 at Muroc Army Air Field in California in 1944 (Jones; Atomic Heritage Foundation).

The man chosen to command the strike force was Lt. Col. Paul W. Tibbets Jr., a 29-year-old bomber pilot who had flown in the first American heavy-bomber raid on occupied Europe in August 1942 and had then spent more than a year test-flying the B-29. On 1 September 1944 he reported to Second Air Force headquarters at Colorado Springs, where Maj. Gen. Uzal Ent and representatives of the Manhattan Project briefed him on the bomb and on the job: to organize, train and command a group that would deliver it in combat (Tibbets; Jones). He was given wide authority to draw on Army Air Forces resources under a priority code word, and he chose as his base Wendover Army Air Field, a remote training field on the Utah–Nevada line, over alternatives in Kansas and Idaho.

The heart of the group was the 393rd Bombardment Squadron (Very Heavy), a B-29 squadron that had been training with the 504th Bombardment Group at Fairmont, Nebraska, and arrived at Wendover on 14 September 1944. Of its 21 crews, 15 were kept for the new mission and organized in three flights of five. The 509th Composite Group itself was constituted on 9 December 1944 and activated on 17 December. It was called “composite” because, unlike a normal bomb group, it contained its own transport squadron, the 320th Troop Carrier Squadron, as well as its own service, engineering, supply, military police and ordnance units, so that it could operate on a forward island with as little outside help, and as few outsiders, as possible (Air Force Historical Research Agency; Atomic Heritage Foundation). At full strength in May 1945 it had 225 officers and 1,542 enlisted men.

The new aircraft were the key to the group’s performance. The first Silverplate B-29s reached Wendover in October 1944, and by the end of the year the group had fourteen training aircraft. In April 1945 the combat aircraft began to arrive from the Martin plant at Omaha: B-29s with fuel-injected engines, reversible-pitch propellers, pneumatic bomb-bay doors that opened and closed in a fraction of the normal time, the bomb bays rebuilt to carry a single very heavy weapon, and all defensive armament except the tail guns removed to save weight. Each bombardier made at least fifty practice drops of inert bomb shapes before the group was declared ready, and the crews practiced the maneuver that followed the release: a steep diving turn of about 155 degrees to put as much distance as possible between the aircraft and the burst (Wikipedia, “509th Composite Group,” citing Campbell; Tibbets).

Tinian and North Field

Tinian was chosen as the group’s base on 24 February 1945. The island, about 39 square miles of flat raised coral and sugar-cane fields just south of Saipan, had been taken by the V Amphibious Corps in the battle of 24 July to 1 August 1944. Of a Japanese garrison of about 8,500, only 313 were captured alive; hundreds of the island’s 15,700 Japanese and Korean civilians were killed in the fighting or took their own lives (National Park Service). Navy construction battalions, the Seabees, landed with the assault troops and began rebuilding the Japanese airstrip before the fighting ended. By the spring of 1945 North Field had four parallel bomber runways, each 8,500 feet long, with hardstands and taxiways for hundreds of B-29s; with West Field at the other end of the island, Tinian was described as the largest airbase in the world. The Seabees laid out its roads on the pattern of Manhattan, which the island resembled in shape, so that the 509th lived and worked off “Broadway” and “Eighth Avenue” (NPS; Wikipedia, “North Field (Tinian)”).

The group moved in stages. An advance party of 29 officers and 61 men flew out between 15 and 22 May. The ground echelon left Wendover by train on 26 April, sailed from Seattle aboard the SS Cape Victory on 6 May and landed on Tinian on 29 May, the official date of the group’s change of station. The air echelon began leaving Wendover on 4 June, and the first B-29 arrived at North Field on 11 June. The 509th took over a former Seabee camp just west of Runway D, with 89 Quonset huts and a warehouse, and fenced it. It was assigned on paper to the 313th Bombardment Wing but took its operational orders directly from Twentieth Air Force headquarters on Guam (Wikipedia, “509th Composite Group,” citing Campbell; AFHRA).

Alongside the 509th worked Project Alberta, the Los Alamos organization formed in March 1945 to prepare the bombs for combat and to assemble them overseas. It was headed by Capt. William S. Parsons of the Navy, the laboratory’s ordnance chief, with the physicist Norman Ramsey as his scientific deputy and Cmdr. Frederick Ashworth as operations officer. On Tinian it numbered 51 people: soldiers, sailors and civilian scientists and technicians, among them Luis Alvarez, Harold Agnew, Philip Morrison and Raemer Schreiber. Brig. Gen. Thomas F. Farrell, Groves’s deputy, arrived to represent Groves in the theater (Wikipedia, “Project Alberta,” citing Hoddeson and others; Jones). The weapons were put together in purpose-built, air-conditioned assembly buildings in a separate, guarded technical area near the north end of the island.

Pumpkins and practice: June and July 1945

Once on Tinian the crews trained again. Between 1 and 22 July they flew fifteen practice missions against Japanese-held islands bypassed by the American advance, including Truk, Marcus and Rota, dropping conventional bombs. Then they began flying over Japan itself. Their weapon was the “pumpkin,” a high-explosive bomb built to the shape, size and handling characteristics of the Fat Man casing, painted orange in its training form. Dropping it singly from high altitude against Japanese cities, followed by the same steep escape turn, gave the bombardiers practice in aiming one very large bomb visually, accustomed Japanese air defenses to small formations of B-29s that did little damage, and tested the ballistics of the casing. Twelve combat missions with 37 sorties were flown between 20 and 29 July, and more on 8 and 14 August; the group was credited in all with 49 pumpkin missions (AFHRA; Wikipedia, citing Campbell). The pumpkins killed Japanese civilians and workers. A study by Japanese researchers has documented the raids city by city, including attacks on Toyama, Nagaoka, Yokkaichi and Tokyo, where one pumpkin landed near the Imperial Palace on 20 July.

Among the other bomb groups on Tinian the 509th had a reputation for living well, flying little and doing nothing, and its fenced compound, its priority on supplies and its single-bomb missions became the subject of jeers and of a mocking poem that circulated in the wing. The crews could not answer it. Very few of them knew what they were training for; the bombardiers and pilots had been told they would drop a bomb of unusual power, and a handful of senior officers knew the rest (Tibbets; Rhodes).

The committees: who decided what

Franklin Roosevelt died on 12 April 1945. Truman, who as vice president had not been told of the project, received his first full briefing from Stimson and Groves on 25 April. Groves’s memorandum for that meeting expected the first gun-type bomb, which he regarded as certain to work without a test, “about 1 August 1945,” and stated plainly that the target had always been expected to be Japan (Groves memorandum of 23 April 1945, in Burr, National Security Archive). From then on the question in Washington was less whether the bomb would be used than how, where and with what accompanying diplomacy. Three groups shaped the answers.

The first was the Target Committee, set up by Groves. It met for the first time on 27 April 1945 at the Pentagon, with Farrell presiding and Air Forces officers and scientists, among them the mathematician John von Neumann and the British physicist William Penney, around the table. Its criteria were practical: a city large enough, more than three miles across, to show the full effect of the bomb; one not yet damaged by conventional bombing, so that the effect could be measured; and one likely to be clear enough for visual bombing in August. It began with seventeen candidate areas, among them Tokyo Bay, Yokohama, Nagoya, Osaka, Kobe, Kyoto, Hiroshima, Kokura and Nagasaki. At its second meeting, in Oppenheimer’s office at Los Alamos on 10 and 11 May, it ranked Kyoto and Hiroshima first, as “AA” targets, with Yokohama and the Kokura Arsenal next, and Niigata also considered. The minutes record arguments for Kyoto that went beyond industry: that as an intellectual center its people were more likely to understand the significance of the weapon. At the third meeting, in Washington on 28 May, the list was Kyoto, Hiroshima and Niigata, and the committee agreed that the bomb should be aimed at the center of the city rather than at an industrial plant (Target Committee minutes, in Burr; Wellerstein, “The Kyoto Misconception,” 2014).

The second was the Interim Committee, appointed by Stimson with Truman’s approval in early May to advise on wartime and postwar policy for atomic energy. Stimson chaired it, with his aide George L. Harrison as alternate; the other members were Byrnes, soon to be secretary of state, as Truman’s personal representative; Ralph Bard, under secretary of the Navy; William Clayton, assistant secretary of state; and the scientific administrators Vannevar Bush, James Conant and Karl Compton. A Scientific Panel of four physicists from the project, Oppenheimer, Enrico Fermi, Arthur Compton and Ernest Lawrence, advised it. At its meetings of 31 May and 1 June 1945 the committee agreed that the bomb should be used against Japan as soon as possible, that it should be used on a war plant surrounded by workers’ homes, and that it should be used without prior warning (Interim Committee notes, in Burr; Hewlett and Anderson). A demonstration on an uninhabited area was discussed over lunch on 31 May and rejected: the bomb might fail, the Japanese might move prisoners into the area, and the United States would have only two bombs ready in August.

In their words

We can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use.

The Scientific Panel’s report of 16 June recorded that scientific opinion was divided, between those who favored a purely technical demonstration and those who favored military use to save American lives, and came down on the side of use. It also urged that Britain, the Soviet Union, France and China be told of the weapon before it was used. One member of the Interim Committee changed his mind. On 27 June Ralph Bard wrote a memorandum proposing that Japan be given two or three days’ warning, and assurances about the Emperor, before the bomb was used, on the ground that the United States’ position as a great humanitarian nation required it. He left the Navy Department at the end of June, and his memorandum did not change the committee’s recommendation (Bard memorandum, in Burr).

The third influence was Stimson himself, and his intervention concerned Kyoto. When Groves met him on 30 May, Stimson asked about the targets and, on hearing that Kyoto headed the list, said he would not approve it. The ancient capital, with its temples and shrines, was the cultural and religious heart of Japan; Stimson had visited it in 1926 and again in 1929. On 1 June he told Gen. Henry Arnold, by his own diary, that Kyoto was not to be bombed without his permission. Groves tried more than once to restore it. At Potsdam, on 24 July, Stimson put his case to Truman: that the bitterness caused by destroying Kyoto might make it impossible to reconcile the Japanese to the United States after the war, rather than to the Soviet Union. Truman agreed (Stimson diary, 24 July 1945, in Burr; Wellerstein). Nagasaki, a port and shipbuilding city with large Mitsubishi works that had been bombed several times on a small scale, took Kyoto’s place on the final list.

Dissent at the Met Lab: the Franck Report and the Szilárd petition

The strongest objections came from the Metallurgical Laboratory in Chicago, where the first reactor had been built (Chapter 2). By 1945 its main work was done, and its scientists had time to think about what came next. In early June a committee chaired by the Nobel physicist James Franck, with Eugene Rabinowitch as principal drafter and Leo Szilárd and Glenn Seaborg among its members, wrote a report on the political and social problems of the bomb. Dated 11 June and forwarded to Washington by Arthur Compton on 12 June, it argued that the United States could not keep its monopoly for long, that a surprise attack on Japan would forfeit public support for international control and start an arms race, and that the bomb should first be demonstrated before observers of the United Nations on a desert or barren island. It reached Stimson’s office, where Harrison summarized it; the Scientific Panel considered its arguments and, as shown above, did not accept them (Franck Report; Harrison memorandum of 26 June 1945, in Burr).

In mid-July Compton asked Farrington Daniels, the director of the Met Lab, to poll the scientists there. Of 150 who answered, the largest group, 46 percent, chose a military demonstration in Japan followed by a renewed chance to surrender before full use; 26 percent preferred an experimental demonstration in the United States before Japanese representatives; 15 percent favored use in the most militarily effective way; 11 percent wanted a public demonstration and no military use; and 2 percent wanted no use at all. The middle option was ambiguous: a “military demonstration in Japan” could mean an attack on a city. Compton reported the poll as support for military use (Daniels poll, in Burr; Hewlett and Anderson).

By the numbers

How 150 Met Lab scientists answered, July 1945

The Farrington Daniels poll at the Metallurgical Laboratory, Chicago, in mid-July 1945. Share of 150 respondents choosing each option, which have been shortened here.

Military demonstration in Japan, then a renewed chance to surrender before full use46%

Experimental demonstration in the United States, with Japanese representatives present26%

Use in the manner most effective militarily, to bring prompt surrender15%

Public experimental demonstration only; no military use11%

Keep the weapons secret and do not use them in this war2%

Leo Szilárd, who had drafted the Einstein letter of 1939 (Chapter 1), went further. He had tried in late May to see Truman and had been sent instead to Byrnes in Spartanburg, South Carolina, where the meeting went badly. In July he drafted a petition to the president, revised it several times, and on 17 July circulated the final text at the Met Lab. It asked Truman to rule that the United States should not use atomic bombs in the war unless the terms to be imposed on Japan had been made public in detail and Japan, knowing them, had refused to surrender, and even then to weigh the moral responsibilities involved. Seventy scientists signed it in Chicago; a few smaller petitions circulated at Oak Ridge (Dannen; Lanouette). Szilárd sent it through official channels, as security required. It went from Compton to Col. Kenneth Nichols, the district engineer, and on to Groves, who held it until after the attack had been ordered; it reached Stimson’s office only after the decision had been made, and Truman did not see it before the bombings. It was declassified in 1961.

The scientists’ dissent has sometimes been presented as a near-revolt, and sometimes dismissed as the second thoughts of a few. Neither is quite right. The Franck Report and the petition were serious documents written by people who knew the weapon better than anyone in Washington, and their warnings about an arms race were borne out. But they were a minority view even in Chicago, they were largely unknown to the scientists at Los Alamos, where Oppenheimer discouraged circulation of the petition, and they arrived after the institutions with authority over the decision had already made their recommendations (Hewlett and Anderson; Bird and Sherwin).

Potsdam: the test, the order and the declaration

Truman sailed for Europe on 7 July for the conference of the Allied leaders at Potsdam, outside Berlin, where he met Stalin and Churchill (replaced by Clement Attlee after the British election results of 26 July). The first report of the Trinity test reached Stimson there on the evening of 16 July; Groves’s long written account arrived on 21 July, and Stimson recorded that the president was “tremendously pepped up” by it (Stimson diary, 21 July 1945, in Burr). On 24 July, after a plenary session, Truman walked over to Stalin and told him, without using the word atomic, that the United States had a new weapon of unusual destructive force. Stalin answered that he hoped it would be put to good use against the Japanese. He already knew a great deal about the project from Soviet espionage at Los Alamos (Chapter 5), and he ordered his own program accelerated (Truman, Year of Decisions, 1955; Holloway, Stalin and the Bomb, 1994).

There was no single meeting at which Truman decided to use the bomb, and no document in which he ordered it. What exists is the operational order. Groves drafted a directive in Washington, it was sent to Potsdam, and Marshall, having obtained Stimson’s approval and, through him, Truman’s, authorized it. On 25 July 1945 Gen. Thomas T. Handy, acting chief of staff in Washington, signed it and addressed it to Gen. Carl Spaatz, commanding the U.S. Army Strategic Air Forces in the Pacific. It directed that the 509th Composite Group, Twentieth Air Force, would deliver its first “special bomb” as soon as weather permitted visual bombing after about 3 August 1945 on one of the targets Hiroshima, Kokura, Niigata and Nagasaki, and that additional bombs would be delivered on those targets as soon as the project staff made them ready (Handy to Spaatz, 25 July 1945, National Archives). The same day Truman wrote in his diary that he had told Stimson to use the weapon so that “military objectives and soldiers and sailors are the target and not women and children.” Historians have read that line in different ways, as self-deception, as a misunderstanding of what a city target meant, or as an honest statement of intent that the target selection did not match (Truman diary, 25 July 1945; Walker; Bernstein).

On 26 July the United States, Britain and China issued the Potsdam Declaration. It called on Japan to proclaim the unconditional surrender of all its armed forces, promised that Japan would not be enslaved or destroyed as a nation, and warned that the alternative was “prompt and utter destruction.” It did not mention the new weapon, and it did not say what would become of the Emperor; a passage that would have allowed a constitutional monarchy under the present dynasty, drafted at Stimson’s urging, had been removed, in part on Byrnes’s advice. The Soviet Union, not yet at war with Japan, was not a signatory. In Tokyo the government, divided and still seeking Soviet mediation through its ambassador in Moscow, decided to make no official reply. On 28 July Prime Minister Kantarō Suzuki told the press that the government would mokusatsu the declaration, a word that can mean to ignore, to treat with silent contempt or to withhold comment; it was reported in the West as a rejection (Butow, Japan’s Decision to Surrender, 1954; Frank, Downfall, 1999).

Behind Japanese policy lay a strategy the Americans could read. Through the Magic intercepts of Japanese diplomatic cables, Washington knew that Foreign Minister Shigenori Tōgō was trying through Ambassador Naotake Satō in Moscow to arrange a visit by Prince Fumimaro Konoe to seek Soviet mediation, that the Emperor wanted the war ended, and that Tōgō insisted unconditional surrender was unacceptable and could offer no concrete terms. Through Ultra intercepts of military traffic it also knew that the Japanese army was pouring troops into southern Kyushu, where the American invasion, Operation Olympic, was planned for 1 November 1945 (Magic summaries of July 1945, in Burr; Frank). How these two streams of intelligence should have been weighed is one of the central questions of the debate taken up in Chapter 9.

USS Indianapolis: the delivery and the loss

The uranium for the first bomb crossed the Pacific by sea and by air. The heavy cruiser USS Indianapolis (CA-35), flagship of Adm. Raymond Spruance’s Fifth Fleet for much of the Central Pacific campaign, had been badly damaged by a kamikaze off Okinawa on 31 March 1945 and had just completed repairs at Mare Island when she was ordered to carry a special cargo. At Hunters Point Naval Shipyard in San Francisco on 16 July, the morning of the Trinity test, a large crate was lashed down in her port hangar and a lead-lined canister was secured to the deck in the flag lieutenant’s cabin, guarded by two Army officers traveling as artillerymen, Maj. Robert Furman and Capt. James Nolan, a radiologist. The canister held the uranium projectile for Little Boy; the crate held the gun assembly and other components. Capt. Charles B. McVay III, the ship’s captain, was told only that every day he saved on the passage would shorten the war (NHHC; Stanton, In Harm’s Way, 2001).

Indianapolis made the run to Pearl Harbor in record time, stopped there briefly on 19 July, and anchored off Tinian on 26 July. Her cargo went ashore by landing craft to the Project Alberta team. The rest of the uranium, the target pieces for the gun, followed by air in the 509th’s own transports at the end of July, and the plutonium core for the second bomb arrived the same way (Wikipedia, “Project Alberta,” citing Hoddeson and others; Jones). From Tinian the cruiser went to Guam and on 28 July sailed alone for Leyte in the Philippines, where she was to train before joining Task Force 95 off Okinawa. She was not escorted; the routing officers considered the route safe, and they were not told of intelligence that Japanese submarines were operating along it.

Shortly after midnight on 30 July 1945, in the Philippine Sea northeast of Leyte, the Japanese submarine I-58, commanded by Lt. Cmdr. Mochitsura Hashimoto, sighted the cruiser in the moonlight and fired a spread of six torpedoes. Two struck the starboard side forward, at about 00:14. The explosions tore away much of the bow, started fires and cut power and communications; the ship rolled over and sank in about twelve minutes. Of the 1,195 men aboard, about 300 went down with her. Some 880 went into the water, many injured or burned, with few life rafts and with life jackets that lost their buoyancy over the following days. Whether a distress signal was sent and received has been disputed ever since; no rescue was launched. Because of a misreading of the Navy’s movement report system, no one ashore reported the ship overdue when she failed to arrive at Leyte on 31 July (NHHC).

The men were in the water for four days and five nights, in groups scattered over miles of sea. They died of their wounds, of exposure and exhaustion, of dehydration, of drinking salt water and the hallucinations it brought, and in attacks by sharks, which survivors described for the rest of their lives. At 10:25 on 2 August Lt. (jg) Wilbur Gwinn, flying a PV-1 Ventura on a routine antisubmarine patrol, saw an oil slick and then men in the water. Within hours a PBY Catalina flown by Lt. Adrian Marks landed on the open sea against orders and took aboard 56 men, packing them on the wings; the destroyer escort USS Cecil J. Doyle and other ships followed, and the search went on until 8 August. Of the 1,195 men aboard, 316 survived (NHHC; Stanton). It was the greatest loss of life at sea from a single sinking in the history of the U.S. Navy.

Ready on Tinian

While Indianapolis was steaming toward Leyte, the Alberta team was finishing the first bomb. The Little Boy assembly used in combat, designated L-11, was complete and ready on 31 July. Test drops of inert Little Boy units had been made off Tinian on 23, 24 and 25 July, and a full dress rehearsal with a unit dropped near Tinian by the aircraft that would fly the mission took place on 31 July. Three Fat Man high-explosive pre-assemblies arrived on 2 August in three B-29s from New Mexico, and the plutonium core had already come by air; one of the pre-assemblies, F31, was set aside for the second attack (Wikipedia, “Project Alberta,” citing Hoddeson and others). The Handy directive allowed an attack from about 3 August; the weather over Japan in the first days of August, with a typhoon to the south, did not.

Spaatz arrived on Guam on 29 July to take command of the strategic air forces in the Pacific and carried the directive with him. The operational order for the first mission, Twentieth Air Force Field Order No. 13, was issued on 2 August, naming Hiroshima as the primary target, Kokura as the secondary and Nagasaki as the tertiary. On 4 August Tibbets and Parsons briefed the crews who would fly, telling them for the first time that the bomb they would carry was the most powerful ever made and showing them, as far as security allowed, what the test in New Mexico had done. The weather forecast for 6 August was good (Rhodes; Wikipedia, “Atomic bombings of Hiroshima and Nagasaki”). The mission is the subject of Chapter 8.

North Carolina had a man in the inner circle of the 509th. The group’s bombardier, Maj. Thomas W. Ferebee, came from a farm outside Mocksville in Davie County, had played baseball and football at Lees-McRae College, and had flown more than sixty missions with Tibbets in Europe and North Africa; Tibbets asked for him by name in 1944 (NCpedia). His story continues in Chapter 8.

Timeline

From Wendover to Tinian, September 1944 – 4 August 1945

1. 1 Sep 1944Lt. Col. Paul Tibbets is briefed at Colorado Springs and given command of the atomic strike force.
2. 14 Sep 1944The 393rd Bombardment Squadron arrives at Wendover Field, Utah.
3. 17 Dec 1944The 509th Composite Group is activated at Wendover.
4. Jan–Feb 1945Ten crews train in long overwater navigation from Batista Field, Cuba.
5. 24 Feb 1945Tinian is selected as the group’s overseas base.
6. 12 Apr 1945Roosevelt dies; Truman becomes president.
7. 25 Apr 1945Stimson and Groves brief Truman on the project.
8. 27 Apr 1945First meeting of the Target Committee at the Pentagon.
9. 9 May 1945First meeting of the Interim Committee.
10. 10–11 May 1945The Target Committee, at Los Alamos, ranks Kyoto and Hiroshima first.
11. 29 May 1945The ground echelon lands on Tinian.
12. 30 May – 1 Jun 1945Stimson strikes Kyoto from the list; the Interim Committee recommends use as soon as possible, on a war plant surrounded by workers’ homes, without warning.
13. 11 Jun 1945The Franck Report is completed in Chicago; the first 509th B-29 lands at North Field.
14. 16 Jun 1945The Scientific Panel sees “no acceptable alternative to direct military use.”
15. 18 Jun 1945Truman approves planning for the invasion of Kyushu, Operation Olympic, for 1 November.
16. 27 Jun 1945Ralph Bard proposes advance warning to Japan.
17. 16 Jul 1945Trinity test in New Mexico; Indianapolis sails from San Francisco with Little Boy components.
18. 17 Jul 1945Szilárd petition signed by seventy Met Lab scientists.
19. 20 Jul 1945First pumpkin-bomb missions over Japan.
20. 24 Jul 1945Truman tells Stalin of a new weapon; Stimson persuades Truman to keep Kyoto off the list.
21. 25 Jul 1945Handy directive to Spaatz: first special bomb after about 3 August on Hiroshima, Kokura, Niigata or Nagasaki.
22. 26 Jul 1945Potsdam Declaration; Indianapolis delivers the Little Boy components at Tinian.
23. 28 Jul 1945Suzuki says the government will mokusatsu the declaration; Indianapolis sails from Guam for Leyte.
24. 30 Jul 1945, about 00:14I-58 torpedoes Indianapolis; she sinks in about twelve minutes.
25. 31 Jul 1945Little Boy unit L-11 is ready on Tinian.
26. 2 Aug 1945Survivors of Indianapolis sighted; Fat Man pre-assemblies arrive on Tinian; Field Order No. 13 names Hiroshima as primary target.
27. 4 Aug 1945Tibbets and Parsons brief the mission crews.

Questions readers ask

Did Truman ever sign an order to drop the bomb?

No single order bears his signature. The operative document is the directive of 25 July 1945, drafted by Groves, approved by Marshall and Stimson at Potsdam with Truman’s knowledge and consent, and signed by Gen. Thomas Handy in Washington. Truman later took full responsibility, and his diary and memoirs make clear that he approved the use of the weapon. Historians such as Barton Bernstein have argued that he inherited a momentum toward use rather than making a fresh decision; others stress that he was briefed, understood the choice and could have stopped it.

Why wasn’t the bomb demonstrated on an empty island first?

The Interim Committee discussed it on 31 May and its Scientific Panel considered it again in June. The reasons recorded for rejecting it were that a dud would be disastrous, that the Japanese might move Allied prisoners to the site, that only two bombs would be available in August, and that a demonstration might not persuade the Japanese military. Critics then and since, including the Franck committee and Ralph Bard, thought a demonstration or at least a specific warning should have been tried.

Why was Hiroshima at the top of the list?

It met every criterion the Target Committee set: a city of some 300,000 people, large enough to show the bomb’s full effect; untouched by the firebombing; flat, with hills on three sides that might focus the blast; the headquarters of the Second General Army and an important port of embarkation; and, the committee believed, the only one of the candidate cities without an Allied prisoner-of-war camp. That last belief was wrong, as Chapter 8 explains.

Did the sinking of Indianapolis have anything to do with her cargo?

No. She had already delivered it, and Hashimoto had no idea what she had carried. The loss was the result of an unescorted voyage through waters where Japanese submarines were known to be active, intelligence that did not reach the people routing the ship, and a reporting system that failed to notice when she did not arrive.

What was a pumpkin bomb?

A conventional high-explosive bomb built in the shape and weight class of the Fat Man casing. The 509th used them for practice in the United States and, from 20 July 1945, in combat over Japan, to give its crews experience with the real flight profile and to accustom the Japanese to small groups of high-flying B-29s. They killed several hundred Japanese in all, according to Japanese local research, and caused damage comparable to a large conventional bomb.

How it connects

This chapter picks up where Chapter 6, Trinity, left off, with the news of the test reaching Potsdam, and it leads directly into Chapter 8, Little Boy and Hiroshima, and Chapter 9, Nagasaki and the surrender. The bombers that flew from Tinian were part of the B-29 campaign told in the Army Air Forces collection, and the islands they flew from were taken in the Central Pacific campaign that also produced the battle described in the Iwo Jima collection; Iwo Jima served as the emergency field and rendezvous point for both atomic missions.

The sinking of Indianapolis by I-58 belongs also to the story of the war under the sea told in the Submarine War collection, and the 509th Composite Group appears among the special units of the war. The project’s whole arc is gathered on the Manhattan Project hub and the World War II page.

Remembering it today

North Field on Tinian, in the Commonwealth of the Northern Mariana Islands, is part of a National Historic Landmark district. The overgrown runways can still be driven, and the two atomic bomb loading pits, re-excavated and preserved under glass, are marked with plaques; the U.S. Air Force began restoring two of the runways for modern use in 2023–2024. Wendover Airfield, on the Utah–Nevada border, keeps the 509th’s hangars and wartime buildings, with a museum run by the Historic Wendover Airfield foundation. The Manhattan Project National Historical Park, created in 2015 at Los Alamos, Oak Ridge and Hanford, tells the story of the people who built the weapons.

The USS Indianapolis National Memorial, a granite monument bearing the names of all 1,195 men aboard, stands on the Canal Walk in Indianapolis and was dedicated in 1995; the survivors and their families held reunions in the city for decades. The Navy’s accounts of the ship and the sinking are kept by the Naval History and Heritage Command. Wreckage and artifacts are not recovered from the wreck, which lies at about 5,500 meters and is protected as a war grave.

Sources

• Vincent C. Jones, Manhattan: The Army and the Atomic Bomb (Washington: U.S. Army Center of Military History, 1985), especially chapters on the 509th and the target decision.
• Richard G. Hewlett and Oscar E. Anderson Jr., The New World, 1939–1946: A History of the United States Atomic Energy Commission, vol. 1 (University Park: Pennsylvania State University Press, 1962).
• William Burr, ed., The Atomic Bomb and the End of World War II: A Collection of Primary Sources, National Security Archive Electronic Briefing Book No. 162 (Target Committee and Interim Committee minutes, Scientific Panel report, Bard memorandum, Magic summaries, Stimson diary, Handy directive).
• Gen. Thomas T. Handy to Gen. Carl Spaatz, 25 July 1945, text at AtomicArchive.com; original in the National Archives.
• Richard Rhodes, The Making of the Atomic Bomb (New York: Simon & Schuster, 1986).
• Leslie R. Groves, Now It Can Be Told: The Story of the Manhattan Project (New York: Harper, 1962).
• Paul W. Tibbets, Return of the Enola Gay (Columbus: Mid Coast Marketing, 1998).
• Richard H. Campbell, The Silverplate Bombers (Jefferson, N.C.: McFarland, 2005).
• Atomic Heritage Foundation / National Museum of Nuclear Science & History, “509th Composite Group” and “Interim Committee”.
• National Park Service, “Tinian Island during the Manhattan Project” and “Wendover Air Base, Utah.”
• Wikipedia, “509th Composite Group,” “Project Alberta” and “North Field (Tinian),” used as guides to the Air Force Historical Research Agency records, Campbell, and Hoddeson et al., Critical Assembly (Cambridge University Press, 1993).
• Alex Wellerstein, “The Kyoto Misconception,” Restricted Data (2014), and “Henry Stimson didn’t go to Kyoto on his honeymoon” (2023).
• Gene Dannen, “Szilard petition, July 17, 1945” (transcription and signers), and William Lanouette, Genius in the Shadows: A Biography of Leo Szilard (New York: Scribner, 1992).
• Kai Bird and Martin J. Sherwin, American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer (New York: Knopf, 2005).
• J. Samuel Walker, Prompt and Utter Destruction: Truman and the Use of Atomic Bombs against Japan, 3rd ed. (Chapel Hill: University of North Carolina Press, 2016).
• Robert J. C. Butow, Japan’s Decision to Surrender (Stanford: Stanford University Press, 1954); Richard B. Frank, Downfall: The End of the Imperial Japanese Empire (New York: Random House, 1999).
• Harry S. Truman, Memoirs, vol. 1, Year of Decisions (Garden City: Doubleday, 1955); David Holloway, Stalin and the Bomb (New Haven: Yale University Press, 1994).
• Naval History and Heritage Command, “USS Indianapolis” remembrance (2024) and Dictionary of American Naval Fighting Ships, “Indianapolis II (CA-35)”; Doug Stanton, In Harm’s Way: The Sinking of the U.S.S. Indianapolis and the Extraordinary Story of Its Survivors (New York: Henry Holt, 2001).
• NCpedia, “Ferebee, Thomas Wilson”.

Photographs: U.S. Army Air Forces and Manhattan Engineer District photographs of the 509th Composite Group and Tinian; a photograph by the Los Alamos physicist Harold Agnew taken as a government employee; Air Force Historical Research Agency files; U.S. Army Signal Corps photographs of the Potsdam Conference; U.S. Navy photographs of USS Indianapolis and her survivors in the National Archives; and the Szilárd petition in the National Archives. All are U.S. government works in the public domain, via Wikimedia Commons. Several are undated within 1945; dates and places not recorded in the original captions are noted as uncertain. Unit insignia drawn for this collection are illustrations, not official emblems.