The gravitation unit (figure 259) is an experimental and not-too-succesful attempt to produce a mine-firing unit which operates on changes in the gravitational effect on a mine due to the transit of a ship over the mine. It was in the idea stage, and was not developed suficiently for production. No samples of equipment have been captured.

The gravitation unit is an idea only, worked out as a result of some calculation made by the Askania Werke in Berlin in cooperation with the Geophysical Institute at Potsdam. The gravitational effect of a ship, measured at P, is of second order. The mass of dis-placed water whose center of gravity is G1 is displaced by the equal mass of the ship whose center of gravity is G2. Because the distance P - G2 is greater than P - G1, there is a difference in gravitational effect at P such that a mass at P with a ship overhead has a smaller weight than the same mass without the ship overhead. This difference in gravity is very small, even when caused by a large ship; but it can be measured by high-presision apparatus of the type used in geophysical research.

The Mechanism. The type of mechanism visualized for this measurement is similar to the Askania gravity balance. Mass M is suspended by spring S. The small gap D between M and the core of inductance L changes slightly when the gravitational effect aorund M is altered. This change in inductance can be measured by standard equipment with high accuracy. If such a mechanism were to be used operationally, some means must be pro-vided to compensate for the temperature effect on the mass, etc. Even is a mine unit with such high precision could be produced, the whole system would be extremely sen-sitive to the natural vibrations of the ground, and would have to be protected against such vibrations by means yet to be devised.

Figure 259 – Schematic Drawing of Gravitation Unit