Serial number 99590 was stamped on April 2, 1947 and cleared final inspection on August 1 that year.
The tuners are probably three-on-a-side D & J (Dinsmore & Jager) #31 machines.
Style 18 features:
Back and sides: Mahogany
Top: Red spruce (Adirondack) - Although Sitka spruce was the norm for Martin guitars at the time, Martin obviously still had some small pieces of Adirondack spruce that could only be used for small body guitars
Binding: Tortoiseshell celluloid
Brazilian rosewood fingerboard
Brazilian rosewood straight bridge
Other period features:
Ebony neck reinforcement
Nickel silver T-frets
"C. F. Martin & Co." decal on headstock
No "Made in USA" stamp on back of headstock
Lower bout: 11-1/4" Upper bout: 8-5/16"
Body length: 15-7/8" Scale length: 21-5/16"
Body depth at neck block: 3-3/16" Body depth at end block: 3-15/16"
Neck width at nut: 1.64" String spacing at bridge: 2.14"
Bridge 5.50" x .096" x 0.34"
Photos and dimensions courtesy Ted Hutson