Designation

The U.S. Navy makes two classifications of Japanese mines. The first covers those that have been recovered and officially identified. The second includes those that have not.

An identified mine carriers a two-letter designation. NAVROD OCLM21-44 dated 8 Sep-tember 1944 statet that the first shall in all cases be J to indicate the nationality and the second letters shall indicate the mine. These letter designations are assigned by the Bureau of Ordnance only.

A mine which has not been thus investigated will be identified by a short fruit name. The circular letter, mentioned previously, provides that field units may assign the name if desired. If the Bureau of Ordnance establishes that the fruit-named mine is a new type, it will assign an appropriate two-letter designation to supersede the temporary appela-tion.

The instruction further authorize the assignment of fruit names to those mines which have not been recovered but are known to exist only through evidence such as captured documents and Prisoner-of-War testimony.

Explosive Charge

Explosive used in Japanese mines recovered or reported to date have been one of the following: Shimose, Type 88, Type 98 and Type 1 Temporary. Shimose and Type 98 are toxic and must never be handled by the bare hands.

General characteristics of the explosive are as follows:

Shimose - Composed of almost pure picric acid. It is used in a cast form in main charges and has a lemon-yellow coloring. It may also be used as a booster charge in a granular or pressed form. Shimose melts at a temperature of 122° to 123° C. Because of impurities which form picrate compounds, Shimose may detonate on rapid heating. It is slightly more powderful than TNT.

Type 88 – Composed of ammonium perchlorate 75%, ferro-silicon 16%, powdered wood 6% and crude oil 3%. It is used in a granular from in main charges, and has a dark grey coloring. The composition of the explosive may vary by 10%. Type 88 decomposes rapid-ly at high temperatures, and is very sensitive to friction. More powerful than TNT, it compares favorably with explosives containing aluminum.

Type 98 – Composed of Hexanitrodiphenylamine 50% and Trinitroanisole 60%. It is used in a cast form in main charges, and has a dark yellow coloring. Type 98's power is approximately that of TNT. It melts at 68° to 70°.

Type 1, Temporary – Composed of Ammonium Picrate 81%, Aluminum 16%, Powdered Wood 2% and crude oil 1%. It is used in a granular powder form in main charges, and is greenish-brown in color. The explosive has a distinctive "oily" odor. It does not melt on heating, but detonates at a temperature of about 300° C. Jap reports indicate that it compares on power with Torpex which is approximately a third more powerfull than TNT.

The explosive described above are sensitive to bullet impact and may detonate when struck by .30 and .50 cal., and 20 mm projectiles. Caution, therefore, should be observed when sinking floating mines by gun fire. CNO has directed that any ship or vessel attem-pting to sink a floating mine by gnfire should not approach closer than 100 yards. Per-sonnel should not be exposed on weather decks since there is danger of being struck by fragments.

The following general safety precautions should be observed when dealing with Japa-nese mines:

Do not bend or damage any horns.

Do not move or jar the mine except from a safe distance.

Do not take a strain on any lines or cables which may be attached externally to the case.

Bear in mind that safety disarming devices may fail to operate as designed.