National made wood-bodied Triolians as early as 1928. They built two that year, then started production of them in 1929. At that time they were also making round- and square-necked tricones, ukeleles, mandolins and tenor and plectrum guitars with German silver. In 1928 they were also making most of those instruments in wood and many of then in tricone (spider bridge) and single cone (bisquit bridge) models. The continued to make some German silver instruments thru 1934, but in 1930 introduced the O style with steel bodies and some brass parts. Most had 12-fret necks, bu some had 14 frets and some necks were made of Bakelite.
In 1931 they also introduced the Duolian model, with painted steel bodies.
The company produced a dizzying array of instruments till a combination of family feuding (the Dopyera brothers), corporate skulduggery, WWII and electric pickups forced the company to fold. It was restarted in the early 1990s and is now producing awesome instruments out of it's California manufacturing facility.
For anybody interested in these instruments, I highly recommend getting a copy of "The History and Artistry of National Resonator Instruments," by Bob Brozman, published in 1993 by CENTERSTREAM Publishing, P.O. Box 5450, Fullerton, CA 92635.
I've got a Style EN (etched N — the one with flat etching all over except mirror-finish nickle around all the edges) that I ordered in September 2002. Love it!