Although nicknamed "Tokyo" tanks, the name was also hyperbole in the fact that no B-17 ever had the range to bomb Japan from any base in World War II.
These fuel tanks consisted of eighteen removable containers, called cells, made of a rubberized compound, installed inside the wings of the airplane, nine to each side.
The Tokyo tanks were installed on either side of the joint (a load-bearing point) where the two wing portions were connected.
Five cells, totaling 270 US gallons (1,000 L) capacity, sat side by side in the outboard wing and were joined by a fuel line to the main wing tank, which delivered fuel to the outboard engine.
B-17s with factory-mounted Tokyo tanks were first introduced to the Eighth Air Force in England in April 1943 with the arrival of the 94th and 95th Bomb Groups, equipped with new aircraft.