'Puran Z' was a Japanese scheme promulgated by Imperial General Headquarters in Tokyo for the creation of a major offensive/defensive strategy in the Pacific (May 1943).
The plan totally ignored the implications of 'Mi' (ii), which had led to the Japanese naval defeat in the Battle of Midway, and also of the implications of the Guadalcanal campaign, which had led to a Japanese land defeat. The plan therefore ordained that a Japanese defensive perimeter should be established along a line from the Aleutian islands group to the Malay barrier via Wake island, the Marshall islands group, the Gilbert islands group, Nauru island, the Bismarck islands group and New Guinea, with defensive garrison bastions located in strategic areas and Admiral Isoroku Yamamoto’s (from 21 May Admiral Mineichi Koga’s) Combined Fleet based at Truk in the Caroline islands group for easy movement to any threatened sector.
In the event of an Allied offensive, the Japanese plan was to draw the attack toward the nearest main force, which would thereupon destroy the attacker with the combination of land-based and carrierborne air power, Allied aircraft carriers and then troop transports being specifically identified as the primary and secondary targets for Japanese aircraft. Should the attackers managed to secure a beach-head, the Japanese defence forces would then under no circumstances allow any inland enlargement and development of the beach-head into an effective lodgement, but were to counterattack until the beach-head had been totally eliminated.
The effect of 'Puran Z' was thus to disperse Japanese forces in a large number of operationally defensive bastions over an area so great that effective supply and reinforcement were next to impossible as US submarine and carrierborne air strengths grew and savaged Japan’s maritime transport capability.
While it made sense to call on the defenders to fight a protracted battle until counter-offensive forces could be rushed in from the nearest main bastion, the Japanese plan made no allowances for the overwhelming US matériel superiority, which permitted them to deal separately with the island garrison and then with any counter-offensive force moving into the area.
Finally, the Americans merely ignored any bastions not on their direct axes of strategic advance, leaving them to be contained by secondary forces (and thus 'to wither on the vine') as the US forces pushed forward to their next major objective. This meant that by the end of World War II the Pacific was dotted with isolated Japanese garrisons which had contributed nothing to Japan’s war effort, and in the process starved and also in many cases suffered dreadfully from the many endemic diseases of the region. These isolated areas included the northern end of the Solomon islands chain, much of the Bismarck islands archipelago, parts of North-East New Guinea and Netherlands New Guinea, most of the Netherlands East Indies, parts of the Philippine islands group, most of the Palau islands group, all of the Caroline islands group, the northern part of the Marshall islands group, the north-western end of the Mariana islands group, the northern element of the Bonin islands group, Marcus island and Wake island.