The Atom Bomb: Making It Happen

IN MAY 1943 CMDR. WILLIAM S. (“Deak”) Parsons returned from a secret mission to the South Pacific, where he had successfully introduced a new weapon in the war against Japan. He expected his next assignment to be the command of a ship. Instead he found himself on a train heading toward a most unlikely posting for a Navy officer: Los Alamos, New Mexico. His traveling companion was a nuclear physicist, J. Robert Oppenheimer.

The name Oppenheimer meant little then outside a limited circle of scientists. Still less known was the Los Alamos laboratory, where Oppenheimer had recently been appointed director. Even those privy to the laboratory’s secrets referred to it obliquely as Project Y of the Manhattan Engineer District. What Parsons learned on his return from the South Pacific was that Los Alamos was working on a new type of bomb with power virtually beyond comprehension—and that he would be intimately involved in building it.

As the train rattled its way west, Oppenheimer and Parsons discussed the officer’s future role among the scientists who were being brought together at Los Alamos. They agreed that the scientists would be entrusted to produce the nuclear guts of the “gadget” (as the bomb was referred to), while Parsons, as head of ordnance, would take charge of transforming their scientific results into a reliable service weapon.

During the next twenty-seven months Parsons would accomplish this and more. Vannevar Bush, the wartime leader of American science, summarized Parsons’s importance: “The fact that [the atomic bomb] came to fruition and into actual use, the fact that the first uses were fully successful … all this was due in no small measure to [Parsons’s] devotion to his task and his high skill in carrying it out.” In wartime instructions Brig. Gen. Leslie Groves, executive head of the Manhattan Project, expressed the same sentiment more tersely: “Don’t let Parsons get killed! We need him.”

The story of the naval officer who transformed the theory of atomic fission into a weapon that ended a war begins with a shy boy of exceptional brilliance. William Parsons was seven years old in 1909 when his father, a lawyer, moved the family from Chicago to rustic Fort Sumner, New Mexico. Fort Sumner was deep in Billy the Kid country and about 150 miles southeast of Los Alamos, then the isolated mountain site of a boys’ school. Young Parsons outperformed his classmates and skipped grades to graduate from high school and pass the Naval Academy examination by age sixteen.

The story of the naval officer who transformed the theory of atomic fission into a weapon that ended a war begins with a shy boy of exceptional brilliance.

In a rather labored pun on his last name, classmates at Annapolis turned “Parsons” into “Deacon,” which was soon shortened to “Deak.” Parsons proved to be an outstanding student in mathematics and physics and graduated from the academy in 1922. Hyman Rickover, who would lead the postwar development of nuclear submarines, was a classmate.

On his first tour of duty, as a gunnery officer aboard the USS Idaho , Ensign Parsons set the tone for his naval career by questioning long-standing assumptions about the dispersal pattern of the fourteen-inch batteries. His analysis was so convincing that it led the ship’s captain to recommend new procedures for the fleet at large.

In May 1927 Parsons’s analytical skills took him to the Naval Postgraduate School, which was then at Annapolis, for advanced studies in ordnance. By this point the social shyness of his earlier days at the Naval Academy had given way to a comfortable modesty. When he spied the beautiful Martha Cluverius on a tennis court, he did not hesitate to challenge her to a set. The tall, slightly balding junior officer appealed to Martha, who was delighted to find him undaunted by the knowledge that her father was an admiral, Wat Tyler Cluverius.

DEAK AND MARTHA married in November 1929, during his reassignment to the Naval Proving Grounds at Dahlgren, Virginia, where he had come to complete a research project. L. T. E. Thompson, a civilian physicist at the proving grounds, recognized Parsons’s brilliance and passion for science and relished his ceaseless questions. In Dr. Tommy, as the physicist was known, Parsons found a mentor who agreed with him that the Navy should look beyond the mere incremental improvement of guns and other conventional weaponry. The next war, they agreed, could be won or lost with weapons yet unknown, and creating these weapons would require ending the indifference with which scientists and officers viewed each other. As long as only a few scientists understood the military environment and only a few officers could speak the scientists’ language, advances would be limited.

Parsons’s ability to speak with scientists was put to the test in July 1933, when the Navy’s Bureau of Ordnance made him its liaison officer to the Naval Research Laboratory (NRL). The NRL was then a little-known facility in Washington, B.C., and Parsons was astounded to learn that Navy brass did not understand the revolutionary possibilities of its investigations into high-frequency radio waves. NRL scientists and engineers had found a way to use such waves to detect ships and aircraft—a system that would later be known as radar—yet only three engineers were pursuing high-frequency studies, and those only part-time. Through the commanding officer, Parsons requested $5,000 to pursue the research full-time. The funds were not approved. None of the Navy’s bureaus saw the detection of airplanes as their business; radio was for communication.

But Parsons’s appeal for support of radar was not in vain. By June 1936, when he went back to sea as executive officer and navigator on the destroyer USS Aylwin, he had passed his zeal to other technical officers. One of these, Rear Adm. F. I. Entwistle, credited Parsons for the Navy’s having operational radar by the time of America’s entry into World War II. From his NRL experience Parsons learned the vulnerability of new ideas to the inflexibility of large bureaucracies.

Scientists who did not know a howitzer from a mortar descended on Washington with weapon ideas and gadgets to test.

In September 1939 Parsons reported back to the Naval Proving Grounds. His arrival coincided with Hitler’s invasion of Poland, which started World War II in Europe. As Dahlgren’s experimental officer Parsons took special interest in a secret device that civilian scientists were developing under the auspices of the National Defense Research Committee (NDRC). Most scientists in American universities had been indifferent, if not openly hostile, to military research, but with Dunkirk and the fall of France in 1940, that changed abruptly. Scientists who did not know a howitzer from a mortar descended on Washington with weapon ideas and gadgets to test.

The NDRC device that intrigued Parsons was the proximity fuze, an ancestor of today’s “smart” weapons. This fuze consisted of a radio transmitter and receiver, the size of a pint of milk, inside an antiaircraft gun shell. The mechanism, glass vacuum tubes and all, had to withstand acceleration of up to 20,000 g’s when fired from a gun. While speeding through the sky, the fuze had to detect the presence of an enemy aircraft and, at optimum distance, trigger the shell’s explosive charge.

Bush asked the Navy to attach “one damn good officer” to the secret project. The Navy assigned Parsons to the management team of the newly formed Applied Physics Laboratory (APL) of Johns Hopkins University. The team’s chief scientist, Merle Tuve, welcomed Parsons. He wrote, “The mere fact that we had a qualified officer with us right in the actual work, knowing every detail, gave everybody confidence that this wasn’t just a silly exercise invented by some civilian.”

After three years of painstaking development, in November 1942 Parsons took 5,000 of the fuzes to the South Pacific for battle trials. An officer in the Solomons campaign recalled: “Parsons came to see if he could get these things battle tested. … We weren’t anxious to go looking for trouble. But he came out there saying, ‘Come, let’s go; let’s go get into a fight.’”

On January 5, 1943, aboard the light cruiser USS Helena , Parsons watched as four Japanese Aichi dive bombers broke formation and attacked the American task force. Defying hundreds of antiaircraft rounds with conventional fuzes, the enemy bombers struck a cruiser and scored two near misses. The attackers were flying away unscathed when one of them streaked by the Helena . Two salvos from a five-inch battery firing shells equipped with proximity fuzes sent the plane into the sea ablaze. The new smart fuzes had succeeded in their first battle encounter.

The proximity fuze came along soon enough to counter Japanese kamikaze attacks and German V-I buzz bombs. When adapted to artillery shells, it would help blunt Hitler’s counteroffensive in the Battle of the Bulge. The military man most responsible for winning these battles against time was Deak Parsons.

Upon returning from the Pacific in May 1943, Parsons had every reason to expect command of a ship. He had had more than his share of shore duty, and by tradition a line officer in time of war belongs at sea. But tradition cut no ice with President Roosevelt’s Military Policy Committee (MPC), a board of scientists and officers, chaired by the ubiquitous Vannevar Bush, that governed the Manhattan Engineer District.

At the May meeting of the—MPC, General Groves reported on Project Y. Research under way at Los Alamos was aimed at answering the critical question, How much fissionable material would be needed to make an atomic bomb? The previous December Enrico Fermi had built the first selfsustaining chain-reacting pile using an enormous heap of uranium oxide. Now fairly pure uranium 235 metal was slowly becoming available, as was fissionable plutonium. To make bombs from these materials, though, one first had to determine their critical mass—the minimum amount needed to ensure that neutrons from fission would continue the chain instead of simply passing into the outside world. Experimenters and theorists were investigating this question intensely, and there was much scientific discussion and speculation in the air. Until that question was answered, many of the physicists believed it would be a waste of time to try to design the bomb itself.

This worried Groves, who was focused on the project’s ultimate objective: building a bomb. He told the committee, “I need an ordnance officer, particularly in the development of the bomb itself, so that we will have service equipment instead of some dreamchild.” Groves added that he knew of no one available in the Army who could fill the bill.

“Would you have any objection to a naval officer?” Bush asked.

“Not at all, if he’s good,” Groves replied.

Bush recommended Deak Parsons. Rear Adm. William Purnell added, “You can’t get a better man.”

On May 5 Parsons was summoned to the office of Adm. Ernest J. King, commander in chief of the U.S. fleet. King was brief and pithy. As Parsons later put it, he was “plunged into the Manhattan District with a set of verbal orders and a discussion with Admiral King lasting less than ten minutes.” A few days later Parsons was on the train with Oppenheimer.

The physicist and the officer delineated responsibilities, engaged in what Parsons called “a highly satisfactory exchange of philosophies,” and laid out the laboratories, machine shops, and firing ranges of Parsons’s ordnance division—all this before Parsons had seen the site. That train ride opened a highly effective militarycivilian partnership. Scientist and officer alike were driven by a desire to end the war and a belief that the bomb could do it.

Groves summer up Dealk’s value to the project by saying, “Don’t let Parsons get killed! We need him.”

Parsons’s two-week visit to Los Alamos came at a critical time. Recommendations had just arrived from a review committee set up by Groves under Warren Lewis, the dean of American chemical engineering. After inspecting the work under way at Los Alamos in respect to the final objective—a bomb to end the war—the committee had called for major expansion, thereby breaking the last strand in Oppenheimer’s earlier dream of a small think-type laboratory.

Working together, the new military-scientific team of Oppenheimer and Parsons authored a joint memorandum to Groves on May 21 with a detailed plan for expanding Project Y. Most of the additions were for Parsons’s division: 175 specialists in ordnance and engineering, an ordnance laboratory, engineering shops, and test ranges. The other major addition was a chemistry and metallurgy laboratory for the final purification of uranium.

All of Parsons’s involvement in the planned expansion occurred before he was officially transferred to the Manhattan Project. The same was true of his early design work on the bomb that occurred upon his return to Washington. There on June 4 he brought together five ordnance leaders, including his old Dahlgren friend L. T. E. Thompson, who by now was the dean of Navy ballistics experts, and George Chadwick, a seasoned ordnance engineer. Parsons asked them to design a most unusual gun—one that would fit inside a bomb.

Parsons’s request was prompted by a basic consideration in atomic-bomb design. To create an effective explosion, you have to assemble a critical mass—that is, at least the minimum amount needed for a sustained reaction—of fissionable material as quickly as possible. The ensuing reaction releases enormous amounts of energy, which destroys whatever the bomb is dropped on; in the process, of course, it also blows the mass apart. The separate parts of the mass have to be brought together very quickly, to make sure the chain reaction proceeds to the maximum possible extent before the explosion disperses them. If they are not assembled quickly enough, the bomb will fizzle.

A simple way to assemble such a mass in a hurry had already occurred to project scientists: Shoot one subcritical piece of fissionable material into another with a gun. Thompson and Chadwick set to work designing one to the preliminary specifications coming from Los Alamos. They eventually came up with a five-inch smoothbore capable of firing a sixty-pound projectile at 3,000 feet per second.

In mid-June, with the gun-design team already at work, Deak and Martha Parsons arrived at Los Alamos with their daughters, Margaret and Clara. Martha, a daughter and granddaughter of Navy admirals, was used to military bases. But nothing in her experience matched the remoteness of this pine-covered mesa, and never had she seen so much frenzied construction—block after block of newly framed offices, laboratories, and rapid-rise apartments. When the Parsons family arrived, the base employed about 150 civilian and military personnel, not counting hordes of construction workers on contract. The number grew daily. By the end of the war there would be about 5,000 residents, including 1,000 spouses and children.

When Parsons got to the nuclear boomtown, his Ordnance Division joined three previously established scientific divisions: Chemistry and Metallurgy, Experimental Physics, and Theoretical. Edwin McMillan and, later, Lt. Cmdr. A. Francis Birch concentrated on developing the 3,000-feet-per-second gun, which was slated for a design called Thin Man. Calculations revealed that it would have to be seventeen feet long, which made it rather unwieldy. The difficulties ahead were revealed in an early drop test of a scale model: A report from the Naval Proving Grounds described it as “an ominous and spectacular failure.”

Meanwhile a completely different type of device was being tested. Seth Neddermeyer, head of Parsons’s implosion group, had begun blowing up explosives tamped around pipes and metal of various shapes, in an attempt to provide an alternative to the gun. His plan was to surround a core of fissionable material with explosives that would compress it inward. (When a sphere of metal is compressed, its surface area decreases, giving neutrons less of a chance to escape. Using this principle, it is possible to squeeze a subcritical sphere into a supercritical one.) Although later implosion studies focused on spheres, Neddermeyer tried a variety of shapes in his early work.

Neddermeyer did not originate the idea of using implosion, but he was its most persistent advocate. Parsons did not actively oppose the idea, but he had serious doubts about Neddermeyer’s methods. Others did too. L. T. E. Thompson wrote, “It seems to me there is a fundamental difficulty with the system which makes it quite certain to be unsatisfactory.” Richard Feynman, then a young member of the theory group, was more succinct: “It stinks.”

Parsons took a fresh look at implosion in late September 1943, when John Von Neumann, the wizard of many scientific disciplines (see “How Von Neumann Showed the Way,” Invention & Technology , Fall 1990), visited Los Alamos. Von Neumann had recently been working on shaped charges—the use of explosives as precision weapons —at the Navy’s Bureau of Ordnance in Washington, D.C. His visit was timely, because by this point the implosion alternative had acquired new importance. Efforts at several sites to separate fissionable uranium 235 from nonfissionable uranium 238 were not going well, and it was far from certain that enough U-235 could be accumulated to build a bomb. Unless a breakthrough occurred, plutonium, which was produced by irradiating the far more plentiful U-238, might be the only material available in significant amounts.

Unfortunately there was also a problem with plutonium. When it was first isolated and named, in March 1941, its chemistry was a mystery; no one was even sure if it emitted neutrons when it underwent fission. Within a year it became clear that plutonium emits plenty of neutrons—too many, in fact. When you get a critical mass together, it blows apart at the drop of a hat, usually before the energy release has had a proper chance to build up.

Calculations showed that there was no way to avoid this pre-detonation problem with the gun design; doing so would require an unfeasibly large muzzle velocity. If implosion could be made to work, however, it could collapse a core of plutonium into supercriticality much faster than any gun. To make a successful bomb, then, project workers had to either scrape together enough U-235 to use the simple and sturdy gun method or else rely on relatively plentiful plutonium, which would require mastering the problematic implosion method. In the end they managed to do both, but in the fall of 1943, with war proceeding in Europe and the Pacific at a horrifying pace, it was hard to tell if either one could be worked out in time to make a difference.

The difficulty with implosion lay in making the explosive behave properly. Getting a plutonium ball the size of an orange to implode symmetrically is a very tricky proposition, since as any ballistics engineer knows, a charge of explosive does not ignite all at once. As the explosion progresses within the tight confines of the plutonium-bomb shell, it sets off shock waves that interfere with one another. If some parts of the plutonium ball are brought together too early, they will explode before the other parts can come fully into play. The result will be a very expensive dud.

Von Neumann and Parsons closeted themselves in an office with a black-board, agreeing not to come out until they found a solution to the implosion problem. Once they had hashed things out, Parsons joined Von Neumann in advocating a new method known as “fast” implosion. This made use of “lenses”—carefully shaped pieces of high explosive in which the detonation waves would behave differently. By placing the lenses properly, it would be possible to “focus” the pressure from different sections of the explosive and make the implosion proceed symmetrically. That way the chain reaction would occur to the maximum extent possible in the brief time that the ball of plutonium held together. With Von Neumann’s help, implosion got a new lease on life. Thus was born a new bomb, Fat Man, measuring approximately nine feet in length and five feet in diameter.

The difficulty with implosion lay in making the explosive behave properly. Getting a plutonium ball the size of an orange to implode symmetrically is a very tricky proposition.

To try out full-scale models and components of both designs, Parsons formed a field-test group of Los Alamos scientists, military officers, and enlisted technicians. Using a modified B-29 bomber, they began drop tests in March 1944 at Muroc Army Air Base (now Edwards Air Force Base) in California. These tests revealed numerous problems: Models of Fat Man yawed and rolled violently; fuzes failed; three Thin Man models got caught and hung in the plane up to ten seconds after release; and one fell ahead of release onto the bomb-bay doors—a nightmare if it had been a fully armed nuclear bomb. The engineering went little better than the testing. George Chadwick, Parsons’s pick for chief engineer, refused to move to the isolated laboratory site from his home in the Detroit area.

THROUGH ALL THE difficulties, Oppenheimer and Parsons retained confidence in each other. Parsons wrote later, “We had two ingredients essential to success: (1) the compulsion of war, (2) the inspired leadership of Oppenheimer.” Oppenheimer gave his view of Parsons in a January 1945 letter to Groves: “It is impossible to overestimate the value which Captain Parsons has been to the project. … He has been almost alone in this project to appreciate the actual military and engineering problems which we should encounter. He has been almost alone in insisting on facing these problems at a date early enough so that we might arrive at their solution.”

In the summer and fall of 1944 Oppenheimer reorganized the laboratory for the aggressive development of fast implosion. Part of Parsons’s ordnance organization, including engineering for Fat Man, went into a new explosives division under George Kistiakowsky. Parsons was made an associate director, the only high-ranking official of the Los Alamos laboratory in uniform and the only one who was not an eminent scientist. The project depended on the Army Air Forces for bombers, crew, and air support, so Parsons sought an air officer who could work closely with him and the Los Alamos scientists. The Air Forces sent Col. Paul W. Tibbets, Jr., a veteran bomber pilot, to meet with Parsons for project approval and briefing.

Tibbets took charge of a bombardment squadron at Wendover Field in Utah, the new center of flight activities for the Manhattan Project. Flight testing out of Wendover began in October with the arrival of fifteen B-29s modified for the new bombs. By the end of the year, Tibbets’s original squadron became the nucleus of the 509th Composite Group, a unique military entity that had to respond to the often mysterious needs of a secret scientific laboratory. The first items drop-tested by the 509th included inert models of the new Little Boy, a sixfoot gun-type bomb with a muzzle velocity of 1,000 feet per second designed to use U-235.

By March 1945 the scientific and engineering ends of the project were nearing completion, but the uncertainties of implosion had added the need for a full-scale live nuclear test of Fat Man. (The simpler ballistics of Little Boy were considered foolproof enough that no test was needed; besides, there wasn’t enough U-235 available to make a second bomb.) To prepare the way, Oppenheimer again shuffled the organization, forming Project Trinity under Kenneth T. Bainbridge to handle the test and Project Alberta under Parsons to prepare for overseas delivery and use of the bombs. At the same time, Oppenheimer made Parsons a member of the forceful Cowpuncher Committee, which “rode herd” on implosion.

The mission for which he was now preparing would symbolize his role in bringing together talent and knowledge from many sources

From March to June of 1945 Parsons juggled two critical functions. As head of ordnance he spurred the completion of all nonnuclear components, including, among others, fail-safe electronics in the bomb to prevent explosion before the delivery plane had time to escape the blast, reinforcement of Little Boy’s tail assembly, proximity fuzes to detonate the bombs at the optimum altitude above ground for maximum damage, and special armor to protect the bombs against enemy gun fire. Also, to give Tibbets’s crews realistic training, Parsons designed and put into production high-explosive bombs, called Pumpkins, which had the aerodynamic characteristics of Fat Man. As head of Project Alberta he organized one of the most complex technical operations ever undertaken at a distant location in a theater of war. He selected personnel and arranged for their training, and through Norman Ramsey’s delivery group he made sure that everything that would be needed overseas—from screwdrivers to hydraulic lifts to gun-assembly buildings—would be in place when the time came.

In June 1945 Parsons turned his full attention to overseas preparations. The mission for which he was now preparing would symbolize his role in bringing together talent and knowledge from many sources: As weaponeer on the Hiroshima flight he would be a Navy officer on an Army Air Forces plane in charge of a weapon developed by civilian scientists under an Army general.

In February Parsons had sent Cmdr. Frederick L. Ashworth to the Pacific to choose a suitable site for the overseas operation. Ashworth selected Tinian, a recently captured island of the Marianas on which six parallel runways had been rushed to completion for launching massive bombing raids on mainland Japan. (While it was in operation, Tinian was the world’s largest airport.) In April Navy Seabees had begun construction of Project Alberta facilities, including fourteen buildings for bomb assembly, shops, and storage, as well as explosives magazines and loading pits.

Parsons spent much of June in whirlwind travel between the Air Forces installation at Wendover; the secret rocket station at Inyokern, California, and the California Institute of Technology in Pasadena, where explosive lenses were being developed; and naval commands at San Diego, for logistical support from the Pacific fleet. From July 2 to 13 he visited Tinian; then he headed back to New Mexico to watch the test of the implosion bomb.

ON THE EVENING OF JULY 15 , Parsons arrived in the rain at Kirtland Army Air Base. One hundred miles south, at Trinity Site, the first nuclear bomb hung from a hundred-foot tower awaiting countdown. Plans had called for Parsons to fly over the tower moments before the explosion with Luis Alvarez’s instrument team as it dropped pressure gauges by parachute, but poor weather made the mission too risky. The flight could occur, Oppenheimer decided, but no closer to the bomb tower than twenty-five miles.

Before dawn on July 16 Parsons stood behind the pilot of a plane circling the Alamogordo test site. Alvarez knelt between the pilot and the copilot. As the countdown came over the radio, the pilot banked and headed in the direction of the tower. From twenty-five miles away at an altitude of 24,000 feet, they would have a grandstand view of the first display of the awesome power of the atom.

The count droned toward zero. Officers and scientists pulled special Polaroid goggles over their eyes. At 5:29 A.M. , the bomb was detonated. Clouds concealed the initial ball of fire, but neither they nor the darkened lenses could contain the burst of illumination that filled the sky. The sensation, according to Alvarez, was one of intense light covering the whole field of vision. A deep orange-red glow pierced the clouds. Shortly after, they saw a new ball of fire developing. Colors danced across the sky, and a mushroom cloud began to form. After eight minutes the cloud towered an estimated 40,000 feet above the ground.

The goals of Trinity had been achieved. Scientific theories had been proven, calculations had been calibrated, weapon feasibility had been established. President Truman was told that atomic bombs would be available for use against Japan within three weeks.

One week after Trinity, Parsons headed back to Tinian aboard a C-54 with photographs and films of the Trinity test. He immediately took charge of final preparations by the technical group from Los Alamos. In the days that followed, elements of Parsons’s planning came together with the same precision as the bombs themselves:

• • July 23. The first of three dummy Little Boys is dropped near Tinian to rehearse the plane’s breakaway maneuver to escape the bomb’s blast.
• • July 26. USS Indianapolis delivers Little Boy’s gun assembly and U-235 projectile. At Potsdam, Truman, Prime Minister Clement Attlee of Great Britain, and President Chiang Kai-shek of China issue a declaration urging Japan to surrender or suffer “prompt and utter destruction.”
• • July 29. The last of the U-235 target inserts for Little Boy arrive, conveyed as three separate parts in three otherwise empty C-54 cargo planes. Japan declines to accept the terms of the Potsdam Declaration. Parsons requests permission to drop the first bomb as early as August 1.
• • July 29-30. A Japanese torpedo sinks the Indianapolis , resulting in the death of 880 men out of a crew of 1,196.
• • July 31. The 509th completes rehearsals for the first mission. Little Boy is assembled and readied for loading. Brig. Gen. Thomas R Farrell, deputy to General Groves, arrives at Tinian.
• • August 1. The first of three Fat Man dummies is dropped near Tinian to test electronic fuzing and detonators and to rehearse for the live delivery.
• • August 2-3. All hands—and Little Boy—stand ready, waiting for the weather over Japan to clear.
• • August 4, 2:00 P.M. Storms continue over Japan. Crewmen of seven B-29s enter a Quonset hut surrounded by armed military police and are finally told what they have been preparing for. Tibbets discloses that a new weapon equivalent to perhaps 20,000 tons of TNT has recently been tested. “We have received orders to drop it on the enemy,” he says.

Parsons tells the airmen: “The bomb you’re going to drop is something new in the history of warfare. It is the most destructive weapon ever produced. We think it will knock out almost everything within a three-mile area.” Crewmen find it reassuring that Parsons, one of the makers of the new superweapon, will be with them on the mission.

• • August 5. Forecast calls for clear weather over Japan the next day. Preparations proceed accordingly.

Parsons and Farrell face an unexpected last-minute problem. Four B-29s have crashed the night before while taking off from Tinian as part of a mass bombing raid on Japan. The plane with the atomic bomb will have a seven-and-a-half-ton overload. If it crashes on takeoff, Parsons warns, “We could get a nuclear explosion and blow up half the island.” He recommends completing the final assembly of the bomb after takeoff. Farrell, fully aware of Groves’s opposition to in-flight tinkering because of cramped conditions in the bomb bay, asks Parsons whether he has ever done this before. “No,” Parsons responds, “but I’ve got all day to try it.” Farrell agrees to the plan.

• • 2:00 P.M. Little Boy is trailered to the loading pit, and technicians scribble pungent messages to the enemy on the bomb. The Enola Gay (named after Tibbets’s mother) is backed over the pit.
• • 3:00 P.M. The bomb is loaded. Parsons squeezes in behind Little Boy. For two hours he balances himself on an improvised catwalk straddling the bombbay doors. Working by flashlight, he methodically practices the assembly, following an elevenstep list.
• • August 5-6, midnight. Tibbets begins the day with a final briefing. Breakfast follows. To Parsons’s consternation, klieg lights and popping flashbulbs from military photographers documenting the event illuminate the Enola Gay and crew.

Shortly before takeoff, Parsons borrows a .45-caliber automatic from a security agent. In the event of capture the pistol will be the only certain safeguard for the secrets in his head.

• • 2:45 A.M. Takeoff. As the Enola Gay approaches the last hundred feet of runway, Tibbets pulls the overloaded bomber off the ground. Fifteen hundred miles ahead, via Iwo Jima, lies the target, Hiroshima.

Minutes into the flight Parsons nods to the electronics officer, Lt. Morris R. Jeppson. They make their way to the bomb bay. Parsons squeezes in behind the bomb. Jeppson hands him tools and holds the flashlight. As Parsons completes each step, he reports by intercom to the cockpit. His progress is relayed by low-frequency radio to Farrell on Tinian.

• • Around 3:15 A.M. Parsons withdraws his nicked and graphite-blackened hands. The assembly is complete. He and Jeppson return to the bomb’s electronic monitoring panels in the crew compartment.
• • 6:00 A.M. The Enola Gay makes rendezvous at Iwo Jima with two observation and instrument planes, which will accompany it to Hiroshima.
• • 7:30 A.M. Parsons returns to the bomb bay and replaces the green safety plugs with red plugs, arming the bomb. Tibbets begins the climb to bombing altitude.
• • 8:38 A.M. The Enola Gay levels off at 32,700 feet. Jeppson continues to monitor Little Boy’s circuitry.
• • 9:09 A.M. Parsons is standing behind Tibbets as Hiroshima comes into sight. Tibbets asks Parsons to verify the target. He does so, thereby authorizing release.
• • 9:15:17 A.M. A mere seventeen seconds after the scheduled drop time, the Enola Gay bolts upward from the release of its five-ton cargo. “Now it is in the lap of the gods,” Parsons says to himself.

Parsons pulls down his protective goggles and listens intently for the bomb-bay doors to close. If they fail, it could mean disaster; open doors would impede the breakaway turn, which will allow them to escape from the blast. Upon hearing the doors snap shut, he feels intense relief.

Forty-three seconds after the bomb is dropped, a bright purple flash penetrates his goggles. A heavy shock rocks the plane. Someone yells, “Flak!”

“No, no, that’s not flak,” Parsons responds. “That’s it—the shock wave. We’re in the clear now.”

The goals of Trinity had been achieved. Scientific theories had been proven, calculations had been calibrated, weapon feasibility had been established.

A second shock wave follows, caused by reflection of the first one from the ground. Parsons pushes back the goggles and looks toward Hiroshima. He is, as he will say later, “completely awestruck by the tremendous mushroom and dust cloud covering the blasted parts of the city.” He watches as the boiling dust and debris rise to 20,000 feet. He sees a white plume climb upward from the center to some 40,000 feet. He watches “an angry dust cloud” spread over the city.

• • 9:40 A.M. As the trio of planes heads back to Tinian, Parsons sends a coded radio message: “Deak to Farrell: Results in all respects clear-cut and successful. Immediate action to carry out further plans [for a second atomic bomb] is recommended. Greater visible effects than at Alamogordo. Target was Hiroshima. Proceeding to Tinian with normal conditions in airplane.” The results are relayed to President Truman aboard the USS Augusta , returning from Potsdam. Truman approves release of the news to the world, again calling on the Japanese to surrender.
• • 2:58 P.M. After twelve hours and thirteen minutes in the air, the Enola Gay lands on Tinian, ending the world’s first atomic mission.

Cheers rose from two hundred or more officers, enlisted men, and scientists when the Enola Gay landed. As Tibbets led the crew down the hatch, Gen. Carl Spaatz, commander of the Strategic Air Forces, strode forward and pinned the Distinguished Service Cross on the breast of Tibbets’s coveralls. The subsequent award of a Silver Star, a lesser honor, to Parsons stirred this comment from Groves: “There was never any question on the part of anybody [familiar with the mission] but that Parsons was running the show. The only person who did not get that right was apparently General Spaatz.” The Navy also responded, at first, with a half-measure. It promoted Parsons to commodore, a rank one star less than the normal progression from captain direct to rear admiral.

THE DAY AFTER the Hiroshima mission, in the quiet of his tent, Parsons wrote a letter to his father: “Depending on how the Japs felt before there is a definite possibility that this kind of attack may crack them and end the war without an invasion. If so it will save hundreds of thousands of American (and even Japanese) lives.”

Parsons, like Groves, believed it would take the shock of a second bomb to persuade the Japanese to surrender. He sped up the Fat Man assembly line so that the second bomb could be dropped before storms forecast for the scheduled date, August 11. In the meantime American bombers showered Japan with leaflets calling for surrender and warning of more bombs with “the most destructive explosive ever devised by man.” On August 9, with Japan still holding out, the Fat Man implosion bomb destroyed almost half the city of Nagasaki. This time Parsons stayed on Tinian.

“Depending on how the Japs felt before there is a definite possibility that this kind of attack may crack them and end the war without an invasion."

The following day the Japanese initiated surrender negotiations. With their formal surrender on September 2 aboard the USS Missouri , the wartime mission of the Manhattan Project—and the personal objective of its ordnance chief, Deak Parsons—was fulfilled.

Two days after the surrender the Navy Department awarded Commodore Parsons the Distinguished Service Medal for exceptionally meritorious service in the development of the atomic bomb. On January 8, 1946, it finally promoted him to rear admiral, a rank not usually given to a line officer without a sea command.

Parsons’s immediate positions in postwar Washington included stints as the Navy Department’s director of atomic defense, Navy representative to the military liaison committee of the Atomic Energy Commission, and deputy chief of the Armed Forces Special Weapons Project. In all these roles he spearheaded the development of the Navy’s postwar nuclear policy. As the master link between science and the military, he profoundly influenced the structure and operating philosophy of today’s Navy laboratories.

Between January 11 and August 18, 1946, Parsons, as deputy to the commander of Operation Crossroads, provided technical direction for the testing of two atomic bombs, one an air burst and the other underwater, in Bikini atoll. He held a similar position two years later in Operation Sandstone, a series of three atomic tests at Eniwetok, making him the only person to witness seven of the first eight atomic explosions.

Parsons never fulfilled his desire to have a ship of his own, but in 1951 he commanded Cruiser Division Six in the Atlantic and Mediterranean. In 1952, as deputy chief in the Bureau of Ordnance, he promoted innovative development programs, including the Bumblebee beam-riding guided missiles and the heathoming Sidewinder. He influenced the establishment of the Navy’s postwar laboratories on a foundation of military-scientific cooperation.

On December 4, 1953, Parsons learned that Robert Oppenheimer’s security clearance was to be suspended. Parsons, so long known for his calm demeanor, became, according to his wife, “extremely upset.” He exclaimed, “This is the biggest mistake that the United States could make!”

The next morning, only minutes after arriving at the Bethesda Naval Hospital, Deak Parsons died of a heart attack at age fifty-two.