During the course of World War II the Germans discovered an underwater phenomenon which they termed "Elektroden Effekt". This phenomenon refers to a modulated compo-nent of the galvanic currents which are created in water by the passage of a ship. They there upon undertook research into the causes for such currents. At this point the Ger-man Navy became alarmed at the possibility of the Allies developing a firing device ope-rating on this principle as a countermeasure against U-boats. To frustrate any such de-velopment, they equipped all U-boats with a short circuit between the propeller shaft and hull. Furthermore, they sought to develop a mine unit that would fire on the same principle. However, this research was never completed.

Data.

1. By placing two copper electrodes approximately 100 feet apart under water it was discovered that a ship or submarine passing over these electordes caused an alternating current to flow. It was also found that this current could be amplified into a audible sig-nal, even if the electrodes were placed as far as 950 feet apart. The nechessary ampli-fication gain to create an audible signal was 10⁶ to 10⁷; high-gain amplifications being necessary as a result of the inefficient method of pickup.

2. The galvanic currents from various parts of U-boats were on the order of 30-40 ma. and the modulation 40 per cent. The modulation occurs only if the propeller shaft ro-tates; when it is at rest there is a short circuit and no alternating current component is present. The modulating effect was attributed to the varying thicknesses of oil film on the propeller shaft during rotation.

3. Experiments were carried out to determine the signatures of all classes of ships, U-boats being emphasized. Great difficulty eas experienced in finding the transit point of a ship on signature curves produced. Experimental data including ship signatures are un-available.