This is a customer's nice old wartime 0-18 and it was in for a neck reset, fret level/dress, new bone saddle, and setup. It'd seen an awful lot of work in its past including an old neck reset (which, as one friend's ex-luthier said "it just didn't take"), a probable refret, refinish, new pickguard, and replaced bits of top and back.
Despite all the abuse, the guitar sings gorgeously and has a particularly weird voice -- it's woody and darker than average and has a quite scooped midrange. Scooped midrange is common in Martins but this one sounds downright moody because of it. I like.
One "wartime" feature is a bigger, rounded-V neck shape and "wood reinforcement" in the neck rather than a steel bar. This one has what appears to be a rosewood (rather than ebony, as usual) rod set into the mahogany of the neck under the fretboard, but I only saw the ends of it, so I couldn't be quite sure. Either way, the neck has remained relatively stable.
The newer finish means this puppy shows-off its wood quite nicely. This guitar is light as a feather and vibrates the belly while playing it.
The Brazilian rosewood board has a 14" radius to it.
I'm fairly sure that the bridge is a replacement but it seems well-made! Ebony pins and an endpin have replaced the originals, over time. My new bone saddle is compensated, too, more than the Tusq one that was in it before. I've dialed action in at 1/16" DGBE and 3/32" EA at the 12th fret.
Because the neck seemed to have a tiny upbow with what appeared to be regular lights, I scooped-out the middle strings to a slight lower gauge (more like 11s) to compensate for that.