Japan needed to deliver its empire's resources, not just control where they were produced. Allied attacks on shipping broke that connection.
Overextension means trying to hold more territory than the available forces and supplies can reliably defend. Japan's conquests contained oil, ore and food, but much of this still had to move by ship to factories, fleets and armies. Defending distant islands and long routes spread Japanese troops, ships and aircraft thinly.
Allied submarines and aircraft attacked merchant ships carrying goods and tankers carrying fuel. Sinking a tanker could deny oil to the navy even while Japan still controlled the oil field. Captured island bases also extended the reach of Allied aircraft and ships, making it harder for Japan to defend and supply its scattered positions.
Fuel shortages then restricted training and military operations. Forces with less fuel were less able to protect the remaining shipping, so further losses could deepen the shortage. Japan's wide commitments and Allied attacks reinforced each other: possession of land did not guarantee a usable flow of supplies.
Worked example: Follow the oil from the field to the navy
Japan controls an oil-producing area, but a fleet elsewhere needs the fuel.
- Oil must be produced, loaded into a tanker and delivered to where it can be used.
- If Allied submarines or aircraft sink the tanker, controlling the oil field has not supplied the fleet.
- With less fuel, the navy can carry out fewer operations, including defending supply routes. This explains how shortages could grow while Japan still held producing territory.
Watch out for this
Japan could not suffer shortages after conquering oil-producing territory.
Control of production and access to delivered supplies are different. Shipping losses could break the connection.
Check your understanding
Which evidence best explains shortages even while Japan held resource-producing areas?
- Merchant ships and tankers were lost on the routes between those areas and the forces or factories needing supplies.
- Japan's occupied territory still included oil fields, so fuel must have been reaching its navy.
- Defending a larger area let Japan concentrate more of its limited ships on each supply route.