Defense Files

The Commanding General, Manhattan District Project (Groves), to the Chief of Staff, United States Army (Marshall)1

top secret

Subject: Atomic Fission Bombs

To: The Chief of Staff

It is now reasonably certain that our operation plans should be based on the gun type bomb, which, it is estimated, will produce the equivalent of a ten thousand ton TNT explosion. The first bomb, without previous full scale test which we do not believe will be necessary, should be ready about 1 August 1945.2 The second one should be ready by the end of the year and succeeding ones at . . . intervals thereafter.

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Our previous hopes that an implosion (compression) type of bomb might be developed in the late spring have now been dissipated by scientific difficulties which we have not as yet been able to solve. The present effects of these difficulties are that more material will be required and that the material will be less efficiently used. We should have sufficient material for the first implosion type bomb sometime in the latter part of July. This bomb would have an effect which would be equivalent to about 500 tons of TNT. During the remainder of 1945 it is estimated that we can produce . . . additional bombs. The effectiveness of these should increase towards 1000 tons each as development proceeds and, if some of our problems are solved, to as much as 2500 tons.

The plan of operations while based on the more certain more powerful gun type bomb also provides for the use of the implosion type bombs when they become available. . . . The time schedule must not be adversely affected by anything other than the difficulties of solving our scientific problems. The 509th Composite Group, 20th Air Force has been organized and it is now undergoing training as well as assisting in essential tests.

The time has now come when we should acquaint the Assistant Chief of Staff OPD and possibly one of his assistants and the Chief of Staff of the 20th Air Force, Brigadier General Lauris Norstad with sufficient information so that the formulation of adequate plans and the necessary troop movements may be carried out without difficulty and without loss in security. It is proposed also that General Norstad, who is about to visit the Southwest Pacific, be authorized to give general information to the Deputy Commander 20th Air Force, Lt. Gen. M. F. Harmon, and limited information to the Commanding General of the 21st Bomber Command, Brig. Gen. H. S. Hansell, Jr. I also feel that it would be advisable for Admiral Nimitz to be informed of our general plans in order that we will be assured the essential Navy assistance in the area. This could best be accomplished by means of a letter from Admiral King to Admiral Nimitz to be delivered by one of the naval officers now on duty under my command.

The need for security will be emphasized to the officers whom it is proposed to alert.

I have consulted with General Arnold and he feels the above proposals are desirable.

Your approval is recommended.

L. R. Groves ,

Major General, USA


To S/W I think the foregoing proposal should be approved with your concurrence G. C. M[arshall]

The Sec. of War and the President both read this paper and approved it. 12/30/44 L R G[roves]

  1. A separate typewritten notation dated December 30, 1944, which is attached to this communication, reads: “Pencilled markings made by Secretary of War for emphasis in presentation to the President at our conference in the White House. L. R. G[roves].” The mentioned markings are the underscorings as shown herein.
  2. Stettinius ( pp. 33 34) indicates that he was given information about the atomic bomb by Roosevelt a few weeks before the trip to the Crimea. In response to a telegram dated June 25, 1951, from Senator B. B. Hickenlooper, William S. Considine (formerly with the Manhattan District Project) indicated that a few days before the Yalta Conference he had delivered certain papers to Stettinius at Malta and had discussed their effectuation. In his telegram Considine then stated: “Discussion also involved questions of certainty of explosion, possible date of use and power potential of A-bomb. I advised him that my information from General Groves was that bomb would explode, that Groves had double-checked scientists on this, that probable date would be about August 1st in accordance with statement in August 1944 that bomb would be ready in year and that explosion of bomb would wreck a large city.” (Military Situation in the Far East, Hearings before the Committee on Armed Services and the Committee on Foreign Relations, United States Senate, 82d Cong., 1st sess., pt. 4, p. 3120.) It has not been possible to identify with certainty the papers that Considine delivered to Stettinius at Malta. No available records, however, contain any indication that atomic-energy matters were discussed with the British at Malta or with either the British or the Russians at Yalta.