[TankerKC]

USAF has been flying the KC-10 hot and heavy for decades - that's also a modified ex-commercial aircraft and I'm not aware of any serious structural issues.

I'd call the KC-10 a derivative of the DC-10. None of the KC-10 airframes were previously airlines. They were built and sold directly to the USAF as airiel refulers. The article makes it sound like these fire tankers are old airliners.

[norton]

Both users and Boeing call it a modified DC10 freighter.

Modifications were done in production, apparently not to already completed aircraft, but it's still about 90% a DC10 freighter. (There have been suggestions about pulling some retired DC's out of mothballs and doing it over again)

"Derivitave" certainly but we're parsing.