When Martin refined the dreadnought design in the '30s, they absolutely revolutionized the acoustic guitar. The rosewood and mahogany dreadnoughts produced powerful tone unlike earlier guitars, and their driving sound was better suited for the musicians of the era.
In those days, the Style-28 rosewood dreadnought had iconic Herringbone purfling around the top edge. Since then, that Herringbone trim has known been a sign of robust Martin dreadnought tone, so much so that a good '30s D-28 is often called a "Herringbone."
In 1976, Martin introduced the Standard Series HD-28, which revived the Herringbone trim and—unlike the regular D-28—had scalloped braces. In modern-day Martin specs, Herringbone and scalloped braces typically go together, and this model is largely responsible for that tradition. Like everything else, it goes back to the '30s. All of the best original prewar Herringbone dreadnoughts have scalloped braces, and in general scalloped braces produce more volume and low-end.
This 1982 Martin HD-28 has been nicely preserved over the years. It shows some general play wear here and there (see photos), but apart from an occasional string change, this HD-28 hasn't been bothered much. It is in very much the same shape as when it left Nazareth in '82, and it includes its original hardshell case.
This 1982 HD-28 has a 1-11/16" nut width and a full-feeling neck profile that has a soft V shape. The frets are in excellent shape, and the current setup is manageable with Medium gauge strings (.100" on the bass E, .080" on the treble E). There is some saddle remaining to lower the action, but for flat-picking or a heavy right hand, it's nice where it is. 1982 the year before Martin switched over the adjustable truss rods, so the saddle will be the best way to bring the action lower.