Slim quickly got on with the task of training his new army to take the fight to the enemy. His basic premise was that off-road mobility was paramount: much heavy equipment was exchanged for mule- or air-transported equipment, and motor transport was kept to a minimum and restricted to vehicles that could cope with some of the worst combat terrain on Earth. The new doctrine dictated that if the Japanese had cut the lines of communication, then they too were surrounded. All units were to form defensive 'boxes', to be resupplied by air and assisted by integrated close air support and armour. The boxes were designed as an effective response to the tactics of infiltration practised by the Japanese in the war. Slim also supported increased offensive patrolling and night training, to encourage his soldiers to lose both their fear of the jungle and their belief that Japanese soldiers were better jungle fighters. He also instructed them to hold their positions once outflanked.