Explosives detonated in contact with thick steel plates produce much deeper holes in the steel when there is a cavity in the explosive in contact with the plate. While this phenomenon has been known for more than 150 years, the enormous increase in penetrating power that can be produced by lining the explosive cavity with thin metal has been discovered only recently. During the war a number of light, low velocity, antitank weapons (e.g., the rocket-propelled Bazooka) were developed which made use of this phenomenon to perforate thick armor plate. A fairly complete mathematical theory of this essentially new phenomenon is presented together with some of the experimental data that aided in the formulation and testing of the theory. The process is separated into two phases: first, the formation of part of the metal liner into a long thin jet traveling longitudinally at very high velocities (30,000 ft./sec.) and, second, the forcing aside of the target material by the extremely high pressures (0.3-million atmos.) produced by the impact of the high speed jet. The theories of both of these phases are based upon the classical hydrodynamics of perfect fluids, which is applicable because the strength of the metals involved can be neglected at the high pressures encountered.

Experimental results are reviewed fo I" C, N', measurements were made at r o t or e, o, i theCo-0 room emperature. In the case -»i and Ni -Cu alloy series. M t f th ase of Ni, data are available from about 10'K

An article by Birkhoff, MacDougall, Pugh, and Taylor (see reference 1) presented hydrodynamic theories of jet formation and target penetration by explosives with lined conical cavities. However, it was unable to explain satisfactorily why the jets produced are several times as long and, therefore, several times as effective as the steady-state theory predicts. It is shown here that these difficulties are overcome by assuming a variable instead of a constant collapse velocity for the walls of the conical liner. The variability in the collapse velocity produces a surprisingly large change in the process of jet formation.

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Previous experiments have indicated that the Hall e.m.f. depends on intensity of magnetization rather than upon applied field or magnetic induction. Additional evidence is offered, the most important being that provided by a material in which H and B-H are of the same order of magnitude.