Page 27: of Maritime Reporter Magazine (April 2000)

water to cavitate, thus forming a bulk cavitations zone. The water refraction near the surface wave has a vertical velocity. The midget submarine is with- in the cavitation zone and was buffeted by a vertical motion, exposing the con- ning tower and its contra-rotating pro- pellers.

The magnitude of the vertical velocity by explosive gas pulsation will lift an object vertically in the cavitation region.

Extrapolations of the bulk cavitation zone calculated from selected charge size and attack geometry indicated that the midget submarine was within the cavitation region causing the submarine to be launched upward by the explosion.

As the submarine broached near the surface and headed into the oncoming waves caused by the concussion. Water crashed into the propeller disk, forming three distinct rooster-tail sprays syn- chronous with each passing wave. The third smallest rooster tail had dissipated somewhat by the time the photo was taken. This underwater explosion analysis has substantiated the action the midget took and strengthened photo- imagery evidence of the existence of a (Continued on page 83) elapsed time intervals were computed to be 174 seconds (approximately three minutes) after the HELENA was hit.

This substantiated that the combat photo was taken at approximately 0801. (Rudimentary shadow analysis indicat- ed the time was 0801-0803).

As the concussion waves approached the advancing midget, they crashed passed its conning tower onto the con- tra-rotating propellers. Generating three distinct rooster tail sprays, various pro- gressively increase in size from the ear- liest spray, the farthest and smallest.

The distance between each of the roost- er tails was computed and found to coin- cide with the pattern of the propagating waves. Thus enabling to compute the distance between the observed vertical edges of the rooster tail to the midget conning tower and found to be 38 ft., match half of the midget's overall length of 80 ft.

The thinner tracks were a typical char- acteristic of the Japanese Type-97 sub- marine torpedo. Test reports of U.S. conducted torpedo run trials after the war indicated only minimal wake was visible to the overhead flying observa- tion aircraft during the test runs. The thinner tracks characteristically are also indicative that they were more recent with older track defused in time. Thus their convergence in the absence of water splashes and the thinner tracks characteristic lend evidence that a sub- marine was present and fired two torpe- does at the targets.

During an underwater explosion event, the chemical reaction of the solid explosive yields gaseous products and exerts high explosive pressure on the surrounding water. The disturbance (compression shock wave) near the charge propagates radially at three to five times the speed of sound. The sur- rounding water is compressed and attains an extremely high radial velocity.

The compression shock wave reflecting from the free surface results in a tensile reflected wave, causing a region of

April, 2000

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