The steep continental slope of the Red Sea beyond the euphotic zone contains the least known biota of the Red Sea. More knowledge exists on the Red Sea’s deep sea than on this transitional zone between photic and aphotic depth. Since 1981, with the help of the research submersibles "Geo" and" Jago", over 430 dives to a maximum depth of 402 m were carried out at various locations off Djibouti, Sudan, Egypt, and Israel; the topics covered include biology, microbiology, physiology, geology, geophysics, and oceanography. The submersible exploration of the Red Sea’s twilight zone is a new, modern step continuing the classical surface-bound deep-sea expeditions which started in the 19lh Century - of which the Austro-Hungarian "Pola" expeditions were among the first.