Abstract: This relates to improvements in fuel tanks, and most particularly lightweight fuel tanks for aircraft. Complex and heavy internal supports and baffles are replaced by a support and baffle combination which is very simple, has very few bolts, and includes primarily transverse tubular members which are sufficiently large for a person to place the upper part of his body therein and have radiating, transversely elongated openings through which one's arm may pass so as to facilitate inspection and repair should it be necessary of the interior of the tank. The tank is of a double wall construction and includes an inner skin and outer skin separated by a honeycomb core. Along the longitudinal bottom and top of the tank there are defined troughs which are formed by removing the core between the two facing layers. The bottom trough becomes a sump for the tank, while the top trough becomes a head space.