This mine apparently is obsolete; only a few specimens have ever been encountered. It is submarine laid, moored and fired by contact. The Japanese designate it as Type 88, Modification 1.

The mine may be laid in water with a maximum depth of approximately 1476 feet; the case depth can be set to a maximum of 66 feet. Japanese documents state that the mi-nimum spacing between mines is 160 feet.

The physical characteristics of the mine are as follows:

Case

Shape – Two hemispheres, 33".9 in diameter, joined by a 12" cylindrical mid-section.

Color – Black.

Mateial - Steel.

Charge – 396 lbs. of block-fitted Shimose.

Total Weight – 847 lbs.

External Fittings

Horns – Four, electrochemical, equally spaced about the upper hemisphere and 16" from the top center of the mine.

Cover Plate – 12".75 diameter, in the center of the upper hemisphere, secured by 16 bolts. In place of the plate, the mine may be fitted with a circular pan 17" deep.

Arming Switch Housing – 5" diameter, on the mid-section, 2".75 below upper hemis-phere, secured by a keep ring.

Detonator Carrier – 5" in diameter, in the center of the lower hemisphere, secured by a keep ring. It protrudes about 2" from the mine case.

Lifting Lugs – Two, on the upper hemisphere, 180° apart and 7".75 from the center.

Depth-taking Hydrostat – 12" long, bolted to an extension on the mooring bail.

Mooring Bail – A 27" span, bolted to two lugs on the lower hemisphere.

Mooring Pulley – 6".25 in diameter, attached to the mooring bail.

Come-along – Fitted to the mooring bail and secured by a shear pin.

Mooring Cable – 1476' of 8 mm diameter (0".31) cable, with 492' of 2 mm diameter (0".078) tail rope attached to bitter end on cable drum.

Operation

The detonator is manually housed in the booster prior to laying. Upon being launched from a submarine, the assembled mine and anchor sink to a depth of 328' where they se-parate. In less than 328' the mine and anchor separate some time after the assembly reaches the bottom. Mooring cable than reeves out of the anchor, over the mooring pulley, and through the depth-taking hydrostat with the bitter end secured to the an-chor. At a pre-set depth, the hydrostat clamps the cable to moor the mine. Fifteen to twenty minutes later, the spring-loaded arming switch closes, delay being caused by an oil dashpot. It should be noted that there are two cables descending from the mine when it is moored, one taut and the other slack.

The mine fires when one of the horns is bent sufficiently to break its glass vial there-by allowing an electrolytie solution to run into a battery cup generating sufficient current to fire the detonator.

Safety Precautions

The JA is designed to disarm, if the mooring cable breaks, by having a come-along pull out the detonator carrier when the mooring cable reeves back through the hydrostat and over the mooring pulley. The design, however, is by no means dependable and the mine should always be assumed to be in dangerous condition if found adrift or on the beach.

Figure 1 – Cross-sectional drawing of mine Type JA

Figure 2 – JA mine without anchor.

Figure 3 – JA mine, flaoting, with its mooring cable cut.