They plot each patch and hope they never have to return to it. Ice cover that stretched far south of the Aleutian Islands forced the sub to run the entire straight submerged, forgoing occasional position fixes from global navigation satellites. The sea floor through the strait is smooth, he acknowledges, but it gradually rises the farther north one sails - at points reaching depths of only 160 feet. The sub is 52 feet tall from the keel bottom to the top of the stubby superstructure, or sail. Meanwhile, ice pressed south through the strait's choke point in the Chukchi Sea.
Diving planes are at full vertical to prevent damage as the sub surfaces.
The ceiling dropped At one point, Commander Perry says, the crew was forced to ease the sub beneath a keel that left a scant 13 feet above the sail and 18 feet between the ship's keel and the bottom. In other cases, deeper ice keels forced the Hawkbill to run parallel to the formations until its sonar scouted openings the sub could clear. Chief of the Boat Gary Olivi, one of the diving officers, puts it more graphically. In addition to gathering data from 135 probes that will have been launched by the time the cruise completes its 44-day science program, scientists aboard the Hawkbill have been taking water samples to study everything from the microscopic creatures to the characteristics of Arctic Ocean currents and the level of chemical contaminants. The primary goal of this final cruise, however, is to map key features of the Arctic Ocean floor.