Beautiful, sounds and plays excellent/ very rare! C. F. Martin 0-28K Model Flat Top Acoustic Guitar (1928), made in Nazareth, PA, natural lacquer finish, koa body, mahogany neck with ebony fingerboard, black tolex hard shell case. 

Starting in the mid/late 1910's Martin began fielding requests to make Hawaiian style guitars, as the craze for native musical stylings had taken hold of the country. After some (in retrospect) quizzical experiments with fan-bracing tops, Martin reverted to the scalloped X-bracing pattern used on the standard guitars, beefed up just a bit for steel strings. Hawaiian koa was used for the body in place of the traditional woods. While many were intended for use as lap-style instruments, the early examples were fretted and set up in standard style with a nut elevator used to adapt them for steel playing as needed.

The 0-28K was a more deluxe model, first shipped in 1918 but not officially cataloged until 1923. This one dates to late 1928, one of only 75 shipped out this year; 641 was the total production run for the model from 1918 up into the 1930s. After the mid-20's Martin began to usually ship them in a dedicated Hawaiian mode for lap-style play. As Hawaiian bands used guitars for rhythm as well as lead, same group could sometimes order identical models with differing set ups. Martin's koa models were somewhat more expensive than standard models in any given style; this guitar listed for $75 (without case) in 1928, which was a fairly substantial sum at the time. The company imported the woods from Hawaii, usually using an intermediary on the west coast but the process must have added considerable expense. Early koa Martins like this are really a connoisseur's delight, a different and distinct flavor of the best small body flat tops ever made and especially favored for fingerpicked and, as intended, Hawaiian styles. This one plays perfectly with a lovely and quite powerful sound and looks simply fantastic, a visual symphony in koa.
 
Overall length is 38 1/8 in. (96.8 cm.), 13 5/8 in. (34.6 cm.) wide at lower bout, and 4 3/16 in. (10.6 cm.) in depth at side, taken at the end block. Scale length is 24 3/4 in. (629 mm.). Width of nut is 1 15/16 in. (49 mm.).