Page:Popular Science Monthly Volume 92.djvu/871

 Popular Science Monf/ili/

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��jectile; second, its prolonged exposure while in the air to the deviating sweep of the wind; third, the fact that a slight roll of the gun platform will greatly change the arc of travel and, therefore, the range of the shell; and, finally, that the target offered by either the periscope or the conning tower of a submarine under way is a mark that is very hard to "range" accurately. These points are mention- ed in order to emphasize the advan- tages of the Isham type of diving or torpedo shell which can be fired over a flat t r a- jectory like any ordinary projectile from a naval gun.

The Isham torpedo shell was original- ly intended to attack the under -water body of an armored ship and thus to reach her vitals. In the invention's present form we see a shell especially and peculiarly suited for battling with U-boats at long range even though the enemy craft offer but the smallest possible mark — the exposed tip of a periscope.* Three years ago the Isham shell was tested by a board of naval officers, and v/hile the fuse did not function satisfactorily in its entirety it showed even then that the designer was working in the right direction. The projectile, however, demonstrated that its author, by employing an unusual type of nose, could make the shell dive, on striking the water, and thereafter pursue a submerged course at a gradually in- creasing depth below the surface.

It Dives and then Explodes

The trial board reported that "a high explosive shell is an urgent necessity for naval use in addition to the armor- pierc-

���The missiles fall all about the U-boat and form a veritable subaqueous barrage — an under- water curtain of fire

��ing shell now adopted." And the same commission stated:

"It would he liit,'li!y (iesiriil)Ic to have a high- explosive shell liaviiif,' a fuse sueli as has been sug- fiesteil hy Mr. Isham, viz, to detonate a shell on strikiiifi thin metal, such as the side of a destroyer, but which in striking' water would not detonate until alter a period of approximately a second — this in order that a shell which struck short of a sliii) might continue its run under water and explode on con- tact with the under - water body or near it."

��Since that time, Mr. Isham has developed a fuse that he declares will do all of the fore- going things and more, i.e., it will explode after a certain time, follow- ing a dive, even should it fail to meet an ob- stacle in its path, and if it hit a solid body, wheth- it will burst within a second thereafter.

��er thick or thin, one hundredth of

When, the projectile impacts with water the momentary checking of its speed fires a time element or "train" of powder which must be consumed before the flame reaches the primer which actually de- tonatesthe high-explosive bursting charge. If it hits either thin or thick plating, a per- cussion cap instantly sets off the prin- cipal mass of high explosive. Hydrostatic pressure does not interfere with the functioning of the fuse. The moment a submarine is seen from afar, the gun will be loaded with the Isham projectiles and hurled at the foe, the missiles forming a veritable subaqueous barrage and creating an under-water curtain fire one or two hundred feet short of the target, so that the shells may strike the body of the submarine and explode or, failing in this, be detonated like so many mines near by and wreck the undersea craft.

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