Project FAMOUS was organized to provide data on the details of the spreading process of the Mid-Atlantic Ridge. From 1971 until 1974, when a series of manned submersible dives to the inner rift valley floor took place, numerous cruises were undertaken to define the chief characteristics of the American and African plates and the line of their common origin. New technology was required and used on several cruises. At the same time, major outfitting of submersibles and training of scientists and pilots for submersible diving were undertaken.
A detailed picture of the inner rift valley has emerged between two fracture zones at latitudes of about 36°30′ and 37°N. The width of the inner valley floor here is approximately 1 to 5 km, with the narrow part nearly midway along this 40-km-long inner valley. There is a series of low, apparently young hills along the center line of the valley floor, which are intensely fissured. Most of the American submersible dives occurred on the floor of this rift valley between the latitudes of 36°47′ and 36°50′N.
On the north, this rift valley segment is offset approximately 20 km to the east (right laterally) by fracture zone A. The dives by French submersibles were primarily in this fracture zone and in the rift valley floor north of the American dive area.
To the south, the rift valley segment is offset about 20 km to the west by fracture zone B. Two of the American dives took place there. Although in these fracture zones the zone of sheared rocks has a width of nearly 20 km, the currently active part of each fracture zone is less than 1 km wide.