The U.S. Navy has deployed trained dolphins to the Persian Gulf to guard against hostile swimmers getting near coalition ships or port facilities with bombs. Called the "Mk 6 anti-swimmer dolphin system", the dolphins belong to Explosive Ordnance Disposal Mobile Unit 3. This is because the dolphins are mainly trained to search for underwater explosives and mines. About as intelligent as dogs, each dolphin bonds with its handler. Without that bond, dolphins could just wander off and not come back when turned loose to work. Occasionally a dolphin will disappear for a few days, particularly when there are wild dolphins in the area. The exact procedures the dolphins use to deal with swimmers, or underwater explosives, is kept secret, lest potential foes can use that information to defeat the dolphins.