Still orphaned was plutonium, which Lawrence and Compton believed so promising. Compton found his chance to speak for it in early December when Bush and Conant called the members of the Uranium Committee to Washington to announce the reorganization of their work. Harold Urey would develop gaseous diffusion at Columbia, Bush and Conant had decided. Lawrence would pursue electromagnetic separation at Berkeley. A young chemical engineer, Eger V. Murphree, the director of research for Standard Oil of New Jersey, would supervise centrifuge development and look into broader questions of engineering. Compton in Chicago would be responsible for theoretical studies and the actual design of the bomb. “The meeting adjourned,” writes Compton, “with the understanding that we would meet again in two weeks to compare progress and shape our plans more firmly.”
Bush, Conant and Compton went to lunch at the Cosmos Club on Lafayette Square. There the Chicago physicist spoke up for plutonium. He argued that the advantage of chemical extraction rather than isotope separation made element 94 “a worthy competitor.” Bush was wary. Conant pointed out that the new element's chemistry was still largely unknown. Compton recalls their exchange:
“Seaborg tells me that within six months from the time [plutonium] is formed [by chain reaction] he can have it available for use in the bomb,” was my comment.
“Glenn Seaborg is a very competent young chemist, but he isn't that good,” said Conant.
How good a chemist Glenn Seaborg might be remained to be seen. Compton, Conant remembers, went on to argue that “the construction of a self-sustaining chain reaction [in natural uranium — Fermi's and Szilard's project] would be a magnificent achievement” even if plutonium flunked as bomb material; “it would prove that the measurements and theoretical calculations were correct”:
I never knew whether it was this near-certainty of demonstrating a slow-neutron reaction which settled the matter in Van's mind, or whether he was impressed with Compton's faith in the production of a plutonium bomb, against my lack of faith as a chemist. At all events, within a matter of weeks he agreed to Arthur Compton's setting up at Chicago a highly secret project.
Bush had called the Washington meeting on a weekend to accommodate busy men. They had assembled on Saturday, December 6, 1941. Almost immediately they found themselves busier yet.
At 7 a.m. Hawaiian time on Sunday, December 7, 1941, near Kahuku Point at the northernmost reach of the island of Oahu, two U.S. Army privates in the process of shutting down the Opana mobile radar station, an aircraft reconnaissance unit which they had manned since 4 a.m., noticed an unusual disturbance on their oscilloscope screen. They checked and confirmed no malfunction and decided the large merged blur of light “must be a flight of some sort.” Their plotting board indicated a bearing out of the northeast at a distance of 132 miles. More than fifty planes appeared to be involved. One of the men called the information center at Fort Shafter, at the other end of the island, where radar and visual reconnaissance reports were combined on a tabletop map. The lieutenant who took the phone heard the radar operator call the sightings “the biggest… he had ever seen.” The operator did not, however, report his estimate of their number. Both the Army and the Navy had been warned of imminent danger of Japanese attack. The Japanese had convinced themselves that dominance over East Asia was vital to their survival. The American reaction to militant Japanese expansion into Manchuria and China — as many as 200,000 men, women and children were brutally slaughtered by the Japanese Army in Shanghai in 1937 — had been to embargo war materials and freeze Japanese assets in the United States. Aviation fuel, steel and scrap iron went on the embargo list in September 1940 when the Japanese moved into French Indochina with the timid approval of Vichy France. After that the Japanese estimated they could survive no more than eighteen months without access to Asian oil and iron ore. For some time they had prepared for war while continuing to negotiate. Now negotiations had collapsed.
Lieutenant General Walter C. Short, commander of the Army's Hawaiian Department, received a coded message on November 27 signed in the name of the Chief of Staff — George Marshall — that read in part:
Negotiations with Japan appear to be terminated to all practical purposes with only the barest possibility that the Japanese Government might come back and offer to continue. Japanese future action unpredictable but hostile action possible at any moment. If hostilities cannot, repeat cannot be avoided the United States desires that Japan commit the first overt act… Measures should be carried out so as not, repeat not, to alarm civil population or disclose intent.
Short had at option three levels of alert, escalating from “a defense against sabotage, espionage and subversive activities without any threat from the outside” to full defense against “an all-out attack.” He thought it obvious that the War Department message “was written basically for General Mac-Arthur in the Philippines” and chose the limited sabotage defense, Alert No. 1.
Admiral Husband E. Kimmel, Commander in Chief of the U.S. Pacific Fleet, which was based at Pearl Harbor west of Honolulu on the southern coast of Oahu, received a similar but even more pointed message from the Navy Department a few hours later:
This dispatch is to be considered a war warning. Negotiations with Japan looking toward stabilization of conditions in the Pacific have ceased and an aggressive move by Japan is expected within the next few days. The number and equipment of Japanese troops and the organization of naval task forces indicates an amphibious expedition against either the Philippines, Thai or Kra Peninsula or possibly Borneo. Execute an appropriate defensive deployment preparatory to carrying out the tasks assigned.
Kimmel noted the references to other theaters of potential conflict. When he and Short exchanged messages he noted the “more cautious phrasing” of the Army warning. “Appropriate defensive deployment” meant, he thought, full security measures for ships at sea. A surprise submarine attack seemed possible and he ordered the depth-bombing of any submarines discovered in the waters around Oahu.
The Army lieutenant who took the Opana radar call therefore had no expectation of danger. He looked for a routine explanation of the unusual report and found it. The Army paid radio station KGMB in Honolulu to play Hawaiian music throughout the night whenever it ferried aircraft to the Islands, giving its navigators a signal to seek. The lieutenant had heard such music on the radio that morning on his way to the information center. He decided that the radar must be picking up a flight of B-17's. The heading plotted at Opanu was the usual direction of approach from California. “Well, don't worry about it,” the lieutenant told the radar men.
Pearl Harbor is a shallow, compound basin sheltered inland through a narrow outer channel from the sea. A bulge of land, Pearl City, and a mid-basin island, Ford Island, canalize the main anchorage of the harbor into a loop of narrow inlets. In 1941 drydocks, oil storage tanks and a submarine base occupied the harbor's irregular eastern shore. Seven battleships rode at anchor immediately southeast of Ford Island that Sunday morning:
Lieutenant Commander Mitsuo Fuchida of the Japanese Imperial Navy, thirty-nine years old, who wore a red shirt to disguise from his men any blood he might shed and a white
The torpedo bombers divided into groups of twos and threes and dived. The aircrews had prepared
