On the P-51 (sorry, creeping the thread back to WWII), there is a story, (probably apocraphal)about the external fuel tanks, apparently they were made of a 'paper-derived' composite (IIRC a dense, heavy, resin filled, cardboard like material, suitably proofed, with raw rubber interlining and aluminium foil coatings).
The story goes that before they went into service an enquiry went 'up the line' to the technical branch (or whatever it's called)of the USAAF as to the feasibility of these tanks being offered.
Such were the delays caused by distance, burocracy and 'farming out' of the work, that the fighters had been using these 'war economy' tanks for some months before a message came back saying that they wouldn't work.

I can't vouch for the truth, but I always thought it a decent tale.

Regard

Walrus