This guitar is a Herringbone Dreadnought With 35 appointments
C.F. Martin & Company's D 28 guitar was originally a herringbone dreadnought, but over time Martin decided to make those rosewood and spruce dreadnoughts without the specifications and trim that had caused them to sometimes simply be called herringbones. When due to high demand Martin had to once again start making the much more fragile designs of the D 28 that it had become famous for making before and during world war two, Martin had started calling those special instruments HD 28's.
The H stands for herringbone, and the D stands for dreadnought.
First and foremost it's important to realize that essentially the Martin D 28 and the Martin D35 are both dreadnought guitars of exactly the same size and shape that are both completely solid wood constructed instruments with rosewood back and sides and a spruce top. Both are 14 frets clear of the body, and designed to be either fingerpicked or flatpicked with steel strings on them.
The chief difference is that the D-35 has always had a fancy three piece back that looks really cool. The thing is, nobody ever sees the back side of it if it's being played, and being played is the thing that a guitar was created to do.
Guitars were created for SOUND and Play-ability
Who can against the idea that guitars were created to be played?
Guitars were most definitely created to be played and heard, and that is why the herringbone Martin D 28 became the most famous, copied, and sought after acoustic guitar in the world. The herringbone D 28 just sounded so much better than any other instrument except for maybe the D18.
Why did these guitars sound so great? Well, it wasn't the "magic" combination of rosewood and spruce that made the D 28 sound so great, if that were it, then the D35 would have sounded just as good, and there would be no reason to ever create the HD35. The HD 35 is essentially just a pre war construction or recreation of the D28's of old or vintage recreation, but with a three piece back of the D 35.
What is essential to understand with the prefix H or the fact of herringbone trim on a Martin guitar is that by having herringbone trim, the trim also signifies things that can NOT be seen from the outside of the instrument. The herringbone trim of the HD 28 or the HD 35 also signifies that the guitar is a high X construction instrument - in regards to the internal bracing of the guitar, and that the braces are scalloped.
When your guitar is a high X Martin then you've got scalloped bracing. You can have scalloped bracing on a Martin instrument without herringbone trim - and such is the case in instruments like the D18.
High X bracing, scalloped bracing - these things make a guitar fragile, but sound far more wonderful than it otherwise would, with far more sustain and volume. Thus, the HD 35