The rarest and maybe the finest National model, of which only around 20 are known to exist. From late in the company's reign, the model was obviously National's attempt to join the swing-era/archtop band wagon, so to speak. It's unique from all other Nationals in that it is an 18" body, as in the Super 400, it has a resonant thin arched wooden top (body made by Kay, which actually had been building a number of very fine instruments for other companies) and a narrower neck, since the new world of jazz guitarists were tired of the big necks of the '30s.
This one has a Gruhn appraisal: "This guitar would have been built/assembled at National-Valco plant, Chicago, Ill. Very few of these guitars were produced and they are very rare on the vintage market today. The guitar is in excellent condition playing wise/tone etc. ... it has had some professionally done repair at some time in its life. I would value this guitar at $15,000 USD at this time."
This one has the wooden resonator cover-plate, which is especially rare because they often broke during constructiom and were replaced with metal plate.
For an excellent article on this model by Michael Simmons, check out: http://www.fretboardjournal.com/blog/catch-day-circa-1939-national-aragon-de-luxe