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[ Ed. Note: This letter by Albert Einstein reproduced from ASHE News, Feb. 1986, contains an idea on how to improve a WW II torpedo. It was written when he was a consultant to the Bureau of Ordnance during the War. The problem posed to Dr. Einstein was apparently whether it was possible to have the torpedo explode when “at rest” on the side of the submarine — the torpedo having been decelerated in 10 ems distance. But to do the job, because the deceleration solution is impractical, he suggests putting an air space ahead of the “fuse mechanism.”]

January 4th, 1943

Commander Stephen Brunauer
Bureau of Ordnance
Navy Department
Washington, DC

Dear Mr. Brunauer:

You have asked me yesterday to submit to you in writing my proposition to bring about a position or the torpedo parallel to the wall of the ship, before the explosion. In working this out, however, I became aware that the realization of this method is quite impossible. It is impossible, namely, to bring the torpedo to rest in working on it on such a short length which is available; the forces are so tremendous that they must mechanically destroy the torpedo.

If v is the speed of a torpedo of the mass m, the negative accelerating force K, the way or acceleration Δ , then K is given by the equation 1/2mv2 = kΔ

If one puts f.instance

m = 100 kg. = 105g

v = 25m = 2,5 103cm

Δ = 10 cm

lo one gets K 5 3 • 10 – absolute units or 300 weight tons (3 • 10 kg.). It is clear that the structure of the torpedo cannot stand this.

The torpedo has therefore to be brought to explosion before losing its speed. In 0,001 second it makes a way of 2,5 em. To be sure, the explosion should be finished before essential parts of the torpedo undergo deformation. It can f.i. be arranged that the head of the torpedo can undergo a deformation of appr. 10 em, without the rest of the torpedo being mechanically deformed. This frontal part should contain empty space { or a space containing only air) to avoid that its deformation produces a compression wave propagating backwards with great speed. The torpedo-head would then look like this

The empty space has the only purpose to gain a few thousands of a second between the time of contact with the ship’s wall in which the fusemechanism comes into function and the time in which the explosion is finished.

Probably care has been taken already of those circumstances in the construction of the torpedos now in use. I am telling it only because I have no information about it.

With kind regards, sincerely yours,

Albert Einstein

Naval Submarine League

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