23.4% of the A400M's fuel capacity is carried in the centre wing box tank.
Wow! That's fascinating! It was a HUGE effort and hassle to get permission from the certification authorities to make the centerwing section wet in the C-17. They were insistent in not permitting fuel above the passengers' heads, and ours was a military certified airplane. I would have thought that that would be even more difficult in a civilly certified airplane. We even used the example of the BAE-146 airliner which had a high wing and wet wing center section as an argument to allow it in the C-17.
Thanks for the update.