Concert

Concert - aka Alto
This is a scale length of 356mm (14in) to 405mm (16in) and these days usually about 380mm (15in)

The scale length kind of existed since the start of the Ukulele as an instrument because this was the original scale length of the Taropatch Ukuleles. It came about as a recognised separate scale in the 1920's because Martin was finding that the Taropatch it had in its catalogue was disliked because of the difficulty in keeping 8 strings in tune, but liked because its larger size gave it more acoustic volume so in 1925 they started to sell the 4 stringed version and called it Concert scale. The most plausible explanation I have seen for the scale name is that the push for the larger 4 string instrument came from the professional and semi professional players who needed the extra volume for their concerts. As it was tuned the same as the Standard scale length Ukulele and the Ukulele was more a solo instrument than and "orchestral" one, (as in the popular Mandolin and Banjo "orchestras" of the early 20th century, that kind of mimicked the string quartets), musically didn't really come into it so initially it was Standard and Concert Ukulele, because Concert sounded more professional rather than naming along the lines of Mandolin and Mandola. It was only with the advent of the Tenor and the greater acceptance of the C tuning for the larger sizes over the D tuning for the standard that musically there became a difference. Concert then became the battleground with Standard tuned one way (D) and [Tenor]] tuned another (C), but Concert going either way and there not really being a space for an intermediate tuning, (unless you used a C# tuning and that really wasn't friendly to any of the commonly use keys!).

The other argument that did rage far more publicly at the time than the largely academic musical notation, was the actual physical size of a Concert Ukulele. Martin had come up with a premium term for a Ukulele, (Concert was being sold as a premium instrument for professionals, as oppose to an ordinary Standard instrument), but Martin was the only one of the big Mainland makers who had been making Taropatches, so they were the only firm to have the equipment in place, (and I don't know how long it takes to set up new production facilities in a Ukulele factory?) So in 1926 the other makers got a public proclamation from a body that they sponsored, called "the National Association of Musical Instrument and Accessories Manufacturers" to set the "official" Standard Approved size of a Concert as 13¾in (347mm) to 14½in (368mm). This meant that the main Chicago and New York firms biggest offerings were now officially Concerts and Martins Concerts weren't. This may have fooled the ordinary punters but the professionals wanted the bigger size not a shift in goalposts, so some of the bigger firms set up new production lines to produce Ukulele of equivalent size to the Martin Concerts. To keep these legitimate in their official proclamation called them Tenors, (it said a Tenor had a string length - it never actually used the word "scale" - from 14½ (368mm) to 15¾in (400mm) and had no mention of anything bigger), which is why a lot of pre WWII US Ukuleles are called Tenor but are actually Concert size. Martin ignored this proclamation and within 2 years of it they brought out a 17in string length Ukulele which they called a Tenor.

With the decline in the popularity, (and production), of the Ukulele in the 1930's it all became less of an issue. After WWII there was a resurgence in the popularity of the Ukulele in the US, but the world was a very different place. Now electric pickups and amplifiers were far more commonplace, and the Ukulele, even with its new popularity, was no longer seen as a professional instrument. Most players just want something cheap and cheerful they could play at picnics or whenever; and even this kind of use was seriously eroded by the portable radio. The few firms that remained, (most had gone under either with the Wall St crash, the "Great Depression", World War II or just a general decline in Chordophone sales over the preceding decades), had cut back production to their most basic models even before the war because that was all most of the public wanted. The marketing had changes a bit now though and these basic models were all now called Sopranos, not Standard as this made them sound more like serious instruments. Martin was pretty much the only firm to still make others sizes and with the introduction of the Baritone, it needed the intermediate scales to justify this name. Also at this time the fact it was more than 20 years since the initial arguments, and the other sizes had never been that common, it was Martin's idea of string length not the NAMIAM one that became the accepted norm, after all no one but Martin was making them.

Outside of the US the whole debate, including the NAMIAM definitions, was completely ignored. In Europe and the British/French Empires, (which at the time covered pretty much everywhere else in the world the Ukulele was thought of), there was only standard and long scale however there was no attempt at a size definition of standard and long scale usually only meant that the instrument had more than 12 frets to the neck or that there was a "Standard" model in the manufacturers catalogue that it was larger than. Hawaii, which was the only other bastion of Ukulele, had given up trying to compete for the mainland mass market before 1925 so never really got involved in the debate. Hawaiian made was more synonymous with quality on the Mainland so they didn't need too. There were of course Hawaiian made 8 string Taropatch Ukuleles of this size throughout this time but not so much the 4 string ones. A few, more market oriented people, like the Summers Brothers, saw some potential in stocking larger size 4 string Ukuleles for the more discerning visitors in the 1930's but they also knew that the models to emulate were Martins so they followed that sizing, and Kamaka, the only major manufacturer to have Ukuleles in continuous production since 1916, didn't make Taropatchs before WWII and only started making scales other than Soprano in their post war production.

One last thing to say about the evolution of the Concert, originally even though they were physically bigger, they still usually had 12 frets to the body. These days though while some still do have 12 frets to the body, it is fairly common meet the body at the 14th fret.