The B747-400ER options, apart from strengthening issues, give the option of one or two aux tanks at the rear of the forward cargo hold.
Each tank is the size of the full-profile cargo container, but is built in on the production line. Each holding roughly 9.5t of fuel, it is transferred to the centre tank after the tail tank is transferred.
The only [?] B744-ER's are operated by QF who have the single-tank option. However, you can bet the B747-8 will have them well to the fore!!
G'day
