The VK, figures 292, 293, is a spring-driven clockwork that runs for 38 seconds. It is used with the M 1 mine unit and is designed to prvent the mine from firing unless the magnetic influence persists at the end of its preset time.

Operation. The setting dial is set to the deired number of seconds. When the M 1 mine unit is actuated, it causes the clock solenoid to operate, thus starting the clock. One second before the end of the preset time, Cam C (figure 293) opens switch A, which opens the hold-on circuit for about one second. When the hold-on circuit is opened, the needle will come off the firing contacts. However, if magnetic influence is present at the end of the preset time, C will close the firing ciruit and fire the mine. If the mine does not fire after approximately 80 actuations of the VK, switch D closes cam E, thus arming the mine permanently, allowing it to fire normally.

Figure 292– VK II

Figure 293 – VK II, Diagram