JI. The J I unit is an attempt to copy one of the simple British systems. It is a one-look, random-direction device, with a 12-place P.D.M. and detonation-protection. It may be fitted to the BMA II or BMA III mines and consists simply of the necessary induction coil, a sensitive relay, 12-place P.D.M., UES (hydrostatic clock), a vibration-actuated anti-countermining switch, and resistors and a condenser. When the hydrostatic clock runs off, three switches are closed and the circuit is fully armed. If the induction coil de-tects a magnetic signal, it energizes the coil of the relay through two resistors. When the relay closes contact, the battery produces a self-holding current for the relay. The ZK II mechanism is actuated and runs off, during which process the holding current is borken before the cycle is complete. When the ZK II switches over, it switches in the detonator and the protection circuit. A final firing actuation will produce a large surge through the detonator to charge the main condenser. The then fires. If a detonation oc-curs when the ZK II has switched over to put the detonator into the circuit, the result is that a vibration-switch makes contact before the relay can close. Closing of the virbat-ion switch immediately charges the main condenser fully, so that, when the relay makes contact, the resultant surge through the detonator to charge the main condenser is too weak to fire the detonator and self-holding of the relay does not place. It is reported that this blocking condition lasts for approximately one minute.