In unity with the rest of the Martin 15 Series, which launched all the way back in 1939, the Martin D-15 Dreadnought acoustic guitar is made entirely of mahogany. The D-15 is, visually, a far more subtle instrument, lacking almost all embellishment other than a tortoiseshell pickguard and simple dot inlays -- the fingerboard is even unbound. It has also taken on a new identity, being renamed the D-15M in 2010.