Shaped Charge - Munroe Effect

Munroe Effect

The Munroe or Neumann effect is the focusing of blast energy by a hollow or void cut on a surface of explosive.

The earliest mention of hollow charges occurred in 1792. The German Franz Xaver von Baader (1765–1841) was a mining engineer at that time and, in a mining journal, advocated a conical space at the forward end of a blasting charge to increase the explosive's effect and thereby save powder. The idea was adopted, for a time, in Norway and in the mines of the Harz mountains of Germany, although the only available explosive at the time was gunpowder, which is not a high explosive and hence incapable of producing the shock wave that the shaped-charge effect requires.

The first true hollow charge effect was achieved in 1883 by the German Max von Foerster (1845–1905), chief of the nitrocellulose factory of Wolff & Co. in Walsrode, Germany.

By 1886, Gustav Bloem of Düsseldorf, Germany had obtained a U.S. patent for hemispherical cavity metal detonators to concentrate the effect of the explosion in an axial direction.

The Munroe effect is named after Charles E. Munroe, who discovered it in 1888. A civilian chemist working at the U.S. Naval Torpedo Station at Newport, Rhode Island, he noticed that when a block of explosive guncotton with the manufacturer's name stamped into it was detonated next to a metal plate, the lettering was cut into the plate. Conversely, if letters were raised in relief above the surface of the explosive, then the letters on the plate would also be raised above its surface. In 1894, Munroe constructed the first crude shaped charge:

Among the experiments made ... was one upon a safe twenty-nine inches cube, with walls four inches and three quarters thick, made up of plates of iron and steel ... hen a hollow charge of dynamite nine pounds and a half in weight and untamped was detonated on it, a hole three inches in diameter was blown clear through the wall ... The hollow cartridge was made by tying the sticks of dynamite around a tin can, the open mouth of the latter being placed downward.

Although Munroe's discovery of the shaped charge was widely publicized in 1900 in Popular Science Monthly, the importance of the tin can "liner" of the hollow charge remained unrecognized for another 44 years. Part of that 1900 article was reprinted in the February 1945 issue of Popular Science, describing how shaped-charge warheads worked. It was this article that at last revealed to the general public how the fabled Bazooka actually worked against armored vehicles during World War II.

In 1910, Egon Neumann of Germany discovered that a block of TNT, which would normally dent a steel plate, cut a hole right through it if the explosive had a conical indentation.

The military usefulness of Munroe's and Neumann's work was not appreciated for a long time. The application of shaped explosive charges to defeat armor emerged in murky circumstances in the years leading up to World War II. Teams of inventors in Germany (Cranz, Schardin, Thomanek) and Switzerland (Mohaupt) independently promoted shaped-charge designs that were licensed and manufactured in secret war production by Great Britain, Germany and the United States. The development of shaped charges revolutionized anti-tank warfare. Tanks now faced a serious vulnerability from a weapon that could be carried by an infantryman or aircraft.

One of the earliest uses of shaped charges was by German glider-borne troops against the Belgian Fort Eben-Emael.