This is a moored, contact mine with several variations, but the Japanese designations for all models is "Type 93". Up to the present time Type 93, Model 1; Type 93, Model 2; Type 93, Model 3; Type 93, Model 3, Modification 1; and Type 93, Model 4 are known to have been used.

These mines are laid by surface craft as offensive or defensive weapons against sub-marines or surface craft. The maximum depth of water in which they can be planted is 3527 feet; the minimum depth is 25 feet (approx.). The maximum depth of the mine case when moored is 246 feet.

With the exception of the Type 93, Model 3, Modification 1, which is described in detail on page 7, the pysical characteristics of the mines are as follows:

Case

Shape – Spherical, 34" in diameter

Color – Black.

Mateial - Steel.

Charge – Type 93, Model 1 – 220 lbs. Type 88 explosive.

Type 93, Model 2 – 220 lbs. Type 88 explosive.

Type 93, Model 3 – Unknown.

Type 93, Model 4 – 220 lbs. Type I, Temporary explosive.

Total Weight – 484 lbs.

External Fittings

Horns – Type 93, Model 1 – Four, electrochemical, 90° apart around the upper hemis-phere, spaced alternately 16".2 and 11".6 from the top center of the case.

Type 93, Model 2 – Same as Model 1 with an additional 3 spaced equally around the lower hemisphere.

Type 93, Model 3 – Nine, electro-chemical; 4 equally spaced on the upper hemisphe-re, and 5 on bosses equally spaced on the lower hermisphere.

Type 93, Model 4 - Nine, electrochemical; 6 spaced irregularly on the upper hemisphe-re and 3 on bosses in the lower hemisphere.

Cover Plate – Type 93, Model 1 – Two on the upper hemisphere, 180° apart, 13".6 from top center of the case, and one on the lower hemisphere, 18" from botton center of case (Other models believed to be the same).

Base plate – Type 93, Model 1 – 11".75 diameter in center of lower hemipshere (Other models believed to be the same.)

Mooring Spindle and Shackle – Tpye 93, Model 1 – Protruding from the center of the base plate (Other models believed to be the same).

Anchor – 1089 lbs., 33" x 33" x 35".5

Cable – 155 m of 13 mm (.51") or

260 m of 10 mm (.39") or

700 m of 6 mm (.24").

Operation

Shortly after the mine assembly strikes the water upon laying, a metal plummet drops away from the anchor reeling out a plummet cable as it sinks. When the plummet reaches a depth pre-set on the cable drum, the drum locks and the anchor separates from the mine case and sinks, reeling out mooring cable from a drum. Weight of the plummet holds a spring-loaded pawl from engaging a ratchet on the mooring cable drum. When the plummet touches bottom, release of tension on the plummet cord allows the pawl to en-gage the ratchet, locking the rotating drum. The mine is then pulled downward and moors at a depth below the surface equal to the length of the plummet cord. Tension on the mooring sprindle in the mine base plate closes a mooring safety switch and houses the booster charge over the detonator, thus arming the mine.

The mine fires when one of the horns is bent sufficiently to brak its glass vial thereby allowing electrolyte to run into a battery cup and generate suficient current to fire the detonator.

Safety Precautions

The mooring safety switch is designed to open and disarm the mine when tension is removed from the mooring spindle. This feature, however, is not dependable.

"TYPE 93, MODEL 3, MODIFICATION 1"

A moored, contact mine laid by a surface craft either as an offensive or defensive weapon against submarines and surface craft. The depth of water in which the mine may be planted and case depths are the same as Type 93. Thes mine was first recovered on Djaul Island in the Southwest Pacific.

The general characteristics of the mine are as follows:

Case

Shape – Spherical, 34" in diameter.

Color – Black.

Material – Steel.

Charge – 220 lbs. Type 88 explosive.

Total Weight – 500 lbs.

External Fittings

Horns – Has receptacles for eight, electrochemical, 6 irregularly spaced on the upper hemisphere with one on the top cover plate, two on bosses on the lower hemisphere.

Cover Plate – 5".25 diameter, in the center of the upper hemisphere.

Lifting Lugs – Two, on the upper hemisphere.

Base Plate – 11".75 diameter in the center of the lower hemisphere.

Mooring Spindle – Horizontal lever type on the base plate.

Anchor and Cable – Same as "Type 93".

Operation

This mine operates in the same manner as "Type 93" described on the preceding page.

Figure 4 – The spherical JB mine.

Figure 5 – JB mine anchor. The same anchor is suitable for any of the various JB types.

Figure 6 – A cross section of the JB mine.

Figure 7 – The JB Modification 3 Model 1 floating. Note the horn in the cover plate.