[PHJim]

Wiki tells us:
U.S./American/Martin tiple
The tiple was redesigned in 1919 by the American guitar company C.F. Martin & Co. for the William J. Smith Co. in New York and was most popular through the 1920s-40s ukulele craze. This tiple is close in length to a tenor ukulele, but with a deeper body. Unlike a ukulele, it has ten steel strings in four mixed-octave courses of 2, 3, 3, and 2 strings. Manufactured for a half century, the Martin tiple was used in jazz, blues and old-time country bands, and as a louder-volume ukulele. It was tuned similarly to a D-tuned ukulele:

A4 A3 • D4 D3 D4 • F#4 F#3 F#4 • B3 B3. (Wound octave-lower strings are indicated A3, D3 and F#3.) A more recent manufacturer of similar instruments recommends tuning a full tone lower, as mentioned below, similar to contemporary ukuleles.

Martin produced mahogany and rosewood bodied tiples, following a model-identification system similar to its guitars: T-15 and T-17, mahogany top, back and sides; T-18, spruce top, mahogany back and sides; T-28, spruce top, rosewood back and sides; T-45, spruce top, rosewood back and sides, fancy abalone inlay. Martin's tiple production continued off-and-on into the 1970s. [1]


Martin tiple
Similar instruments were made by Regal, D'Angelico and other companies during the early decades of Martin production.

In the 21st century, the Ohana ukulele company began manufacturing an all-mahogany tiple similar to the Martin, but calling it "a vintage ukulele inspired by the Columbian Tiple." The company recommended tuning with the lowest note a C, like contemporary ukuleles. (G3 G4 – C4 C3 C4 – E4 E3 E4 – A4 A4) [2]

Tiple strings and tuning: Guitar-style metal strings are used, and in addition to the original ukulele-style tuning (above) used, the American tiple is reportedly sometimes tuned like the upper four courses of the guitar, presumably with special sets of strings.