Iran began training troops in infiltration, patrolling, night-fighting, marsh warfare, and mountain warfare. They also began training thousands of Revolutionary Guard commandos in amphibious warfare, as southern Iraq is marshy and filled with wetlands. Iran used speedboats to cross the marshes and rivers in southern Iraq and landed troops on the opposing banks, where they would dig and set up pontoon bridges across the rivers and wetlands to allow heavy troops and supplies to cross. Iran also learned to integrate foreign guerrilla units as part of their military operations. On the northern front, Iran began working heavily with the Peshmerga, Kurdish guerrillas. Iranian military advisors organised the Kurds into raiding parties of 12 guerrillas, which would attack Iraqi command posts, troop formations, infrastructure (including roads and supply lines), and government buildings. The oil refineries of Kirkuk became a favourite target, and were often hit by homemade Peshmerga rockets.