An over-all plan to examine all physical laws that might be applied to influence mine units led the Germans to undertake varying degrees of experimentation with the following types of units: optical, cosmic ray, infra red, UEP (Elektroden Effekt), gravitiation, and Wellensonde (Wave probe).

Optical. The Navy devised a number of experimantal optical units. Those designed for use in the open sea presented serious difficulties, and none was perfected before the end of the war. However, a river unit used operationally in the latter stages of the war against river bridges, achieved some success. All these units utilized photoelectrical cells so arranged that decreases in light of prescribed intensity and rate would actuate the unit.

Cosmic Ray. Preliminary development was begun upon a cosmic ray unit that would operate on the increase of the underwater cosmic ray level caused by the passage of a ship. The earliest experiments were conducted with twentyfour standard Geiger-Müller counter tubes cast into the explosive of an LMB mine case. Difficulties in obtaining a sa-tisfactory high potential supply and in regulating this potential slowed the project to such an extent that it was still in little more than the "idea stage" at the war's terminat-ion.

Infra Red. Although the Germans made inquirly into the possible application of the underwater action of infra red rays, no information on the progress in this field was ob-tained by U.S. Naval invesrtigators, and, to date, no reports have been received from British sources.

Underwater Eletrical Potential (Elektroden Effekt). During the course of World War II the German Navy discovered that the passage of a ship created an electrical current in the water which could be detected by copper electrodes placed on the sea bottom. They termed this phenomenon the "Electorden Effect" and sought to develop a mine unit taht would operate on this principle. Progress was slow, and at the close of the war the investigation was still in the preliminary stages.

Gravitation. The Askania Werke, Berlin, attempted to create a mine mechanism that would work on a principle similar to that of the Askania Gravity Balance. The Werke made certain calculations in conjunction with the Geophysical Institute of Potsdam, but the idea made relatively insignificant progress.

Wellensonde (Wave Probe). The Germans sought to untilize the distortion which passing verssels would effect upon high frequency alternating currents emanating from a mine case, in order to fire a unit. The principle was similar to the U.S. Navy's Electrical Discontinuity Discriminator, but the German application never progressed beyond the ex-perimantal stage.