For some years members of the Underwater Demolition Teams of the United States Navy have been carrying out experiments in skin-diving in Arctic and Antarctic waters, with the object of determining the limits of man's endurance in these conditions. The main military purposes of swimming in polar waters are to assist the escape of ships beset in ice by blasting channels out to open water, and to reconnoitre landing beaches which are protected by ice. Secondary operations include inspection and repair of under-water damage to ships and the recovery of submerged equipment.