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1945: Building the Bomb

1945: Building the Bomb

Timeline Image: 
Oppenheimer and Groves

1945 May 28

Target Committee meets with Lt. Col. Paul Tibbets in attendance. The meeting reviews preparation for delivering atomic bombs, and status of conventional bombing of Japan. Tibbets estimates that by Jan. 1, 1946 all major cities of Japan will have been destroyed by fire bombing. The target list is now Kyoto, Hiroshima, and Niigata.

1945 May 25

464 B-29s raid Tokyo again, burning out nearly 16 square miles of the remaining city. Only a few thousand are killed, urban inhabitants have learned to flee fire bomb attacks quickly and escape the flames. Also, Operation OLYMPIC, the invasion of Kyushu (the southern Japanese island), is set for November 1.

1945 May

Little Boy is ready for combat use, except for the U-235 core. It is estimated sufficient material will be available by 1 August.

1945 May 10-11

Target Committee reconvenes. On the committee now are J. Robert Oppenheimer, John von Neumann, Deak Parsons, and Hans Bethe. Meeting discusses issues combat employment of atomic bombs (e.g. proper burst height, etc.). Target list is shortened to Kyoto, Hiroshima, Yokohama, and Kokura Arsenal (Niigata is considered).

1945 May 7

The 100-ton test is conducted. 108 tons of TNT, laced with 1000 curies of reactor fission products, are exploded 800 yards from Trinity ground zero to test instrumentation for The Trinity Test. This is the largest instrumented explosion conducted up to this date. Also, Nazi Germany surrenders to the Allies.

1945 Apr 30

Initiator Committee (Hans Bethe, Enrico Fermi and Robert Christy) selects the most promising design for fission initiator (neutron generator) to be used in the implosion bomb. The "Urchin" design is favored, and work on initiator fabrication begins. Also, first batch of supplies for the atomic bomb deployment leaves for Tinian Island from Wendover, Utah.