-39— and elsewhere, ~! it is clear that the engine necessary for utilizing the explosive, that is, the bomb itself, is a highly intricate anc fairly massive mechanism, The massiveness is not something which we can expect future research to diminish. It is inherent in the bomb, The mechanism and casing surrounding the explosive element must be heavy enough to act as a "tamper," that is, as a means of holding the explosive substance together until the reaction has made substantial progress, Otherwise the materiais would fly apart before the reaction was fairly begun, And since the Smyth Report makes it clear that it is not the tensile strength .of the tamper but the inertia due to mass which is important, we need expect no particular assistance from metallurgical advances, The designing of the bomb apparently involved sgneofjhe major problems cf the whole "Manhattan District" project. The laboratory at Los Alamos was devoted almost exclusively to solving those problems, some of which for a time looked insuperable, The former director of that laboratory has stated that the results of the research undertakenthere required for its recording a book of some fifteen volumes“? The detonation problem is not even remotely like that of any otner explosive, It requires the bringing torether instantaneously in perfect union of two or more subcritical masses of the explosive material (which up to 276 General Arnold, for example, in his Third Report to the Secretary of War asserted that at present the only effective means of delivering the atomic bomb is the "very heavy bomber." See printed edition, p. 68. 28, One might venture to speculate whether the increase in power which the atomic bomb is reported to have undergone since it was first used is not due to the use of a more massive tamper to produce a more complete reaction, If so, the bomb has been increasing in weightrather than the reverse, or* Robert J. Oppenheimer, loc, cit., p. 3.