Albert Einstein to Stephen Brunauer - August 22, 1943
According to the suggestion you expressed in your letter of 19. VIII I am giving you here reasons for my opinion concerning the best localisation for initiation of the Torpedo explosion, Dr. Neumann mentioned to you. The assertion is that the initiation should be made in front (point A fig 1), not in the rear (point B, fig 1).
1. First a general remark of a rav qualitativ character concerning the reaction of a underwater explosion on a deformable wall. 
If there is in ζ (Fig 2) an explosion the expl. pressure gives to a part of the wall (the extension of wich being determined by a certain angle α and the distance h) certain velocities. Those velocities resp. the corresponding kinetic energy is mainly absorbed by a plastic deformation of the plate. If deformation is deep enough the plate will break.
2. The extension of the deformed part of the plate is growing with h, the probability for the production of a hole is diminishing with growing h, the available energy being dispersed over a bigger volume of plate-material.
3. On pictures which were shown to me on your suggestion by Dr. Gorensen I have seen that the broken plates showed often radial lines of fractures (radial slits). This seems to show that the fracture is starting in the central region, extending afterwards radially in producing radial slits. One can also easily understand that maximum plastic deformation will occur in the central part (except in cases where there are weak spots due to the special structure of the wall).
4. It seems therefore reasonable to bring about such a repatition of te explosion pressures (in time and space) that there be first a rather small central hole, wich expands radially in the later phases of the explosion resp. deformation.
If te explosion is initiated in B (Fig 1), the explosion pressures are reaching a considerable part of the wall nearly at the same time. The deformation will from the beginning extend over a considerable area. There will be no tendency to bring about the localized central hole mentioned before. If however the explosion is initiated in A, there will be in the first phase of the explosion a concentration of the biggest pressures on a relatively small area. There will be a probability for a perforation in a small area wich will expand in the later phases of the deformation and radial slits will be produced.
5. According to these considerations it seems reasonable to provide (later) a special device in the front of the Torpedo to secure a perforation of the wall in the first phase of the explosion. This could be brought about through „cavity-effect”
or otherwise trough impact of accelerated masses
I estimate that what I did til now for the Navy may be equivalent to 5 days work. It will be most convenient to send the corresponding money directly to the Institute for advanced study.
With kind wishes yours
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