The full details of the NATIONAL and PORTEX portables have been given some time back in concert with our article surrounding the Harris / Rex / Demountable standard machines.  However, the volume of information available on these machines, coupled with the strong aversion to standard typewriters by many modern enthusiasts indicates a separate entry here about these machines, even with risk of repetition.

As detailed previously these machines took several model numbers, and names but were apparently always produced in the Fond du Lac, Wisconsin plant owned by Rex Typewriter Company throughout their entire production (even though some machines may have been actually shipped out as parts and assembled overseas.)
These machines were the only units built at the aforementioned plant which were not designed by De Witt C. Harris.  Instead, they were the conception of Hubert K. Henry and were assembled through arrangements and rights by Rex.  It seems that while the first incarnation responsible for the sale of the machines was a National Typewriter Co. (early examples are so labeled) the company probably got into trouble and was eventually absorbed by Rex Typewriter.  Later, it also appears that production was separated again, at least on paper, as there are mentions of a "National Typewriter Department of Rex Typewriter Corporation" in historical literature.  At that same time, though, Rex was also making machines not labeled as "National" but as "Portex," a contraction of the names "portable" and "Rex" and selling them through its own channels.  Whatever the actual corporate arrangements and labeling, though, the machine is seen today to be an inexpensively-made, almost brutally simple typewriter almost devoid of operative features (none has a back-space, for example) and representative of that class of portable typewriter which was just barely enough machine to be saleable and operable.  Working with one of these machines is a very primal experience, almost minimalist in nature and certainly these machines when compared with other better-equipped and better built examples from other makers both older and newer fall far short in every quality and category.  Having said that they were actually built rather solidly, for what they were, and are most often found complete and relatively operable (not surprising since there is little equipped and little to break!)  They are sturdier than the roughly contemporary ALLEN machines, as an example.
National No. 2 / serial 1590

Thomas Fuertig collection

We will now display the whole range of variants available to us for display, for the interest of those who enjoy particulars.  The machine seen here is the first introduced.  Note the shift lock lever above and to the left of the keyboard, and the paper fingers on the carriage.
Express / no serial

Thomas Fuertig collection

This Express does not exactly match any known National or Portex variant, and was apparently distributed in Switzerland.  It has a paper bail, although without rollers, instead of paper fingers and a number of other small detail differences.  With the single set of shift keys and shift lock lever we might safely describe this machine as a sub-variant of the No. 2 series.
National B / serial 5516

Tilman Elster collection

This machine is another sub-variant, but it is actually our first example of the National No. 3 series.  Note that shift keys have been added to the right side of the keyboard, and also above these is a shift lock key.  This machine is a sub-variant only because of its model labeling and German keyboard and is thought to have been sold only overseas.
National No. 3 / serial 12681

Tilman Elster collection

The "regular" version of the National No. 3.  This machine displays a round decal on the paper table; labeling and decal design and placement seemingly changed quite often in this series of machines even though the machine itself, in basic form never did except for the shift keys and some of the carriage details.
Portex No. 5 / serial 19552

Tilman Elster collection

The "Portex" name first occurs at serial numbers just over 16,000 in the production run and applies only to No. 5 machines.  Beyond that point in production, machines carrying either the National or the Portex names are mixed relatively indiscriminantly so that little can be ascertained about production.  Both run continuously through the end of known serial numbers.  No. 5 appeared in 1920.

Perhaps the most easily visible change is the sight guide near the print point which is never found on No. 3 models.  On the No. 5, the margin release lever is duplicated, now being on the right side of the carriage as well as the left.
Portex No. 5 / serial 19882

David B. Davis collection

Visible on this Portex No. 5 are levers at either side of the carriage.  These are for margin release, there being no key on the keyboard for such.  There is, and never was on any model, a back-space key or function.  In front of the right side margin release lever is the paper release; below the line-space mechanism, on the left, and near the left-side platen knob is the carriage release.
National No. 5 / serial 20718

Tilman Elster collection

Around this serial number, machines began to appear with wholly nickel plated bodies such as seen here.  The machine itself does not differ.  The "Eagle-N" emblem from the paper table is enlarged below. 
National No. 5 / serial 22036            Will Davis collection. 

One of our two operative examples for the analytical notes presented earlier.
We described these machines as "minimalist" earlier, and one further feature should be noted.  On none of these machines is the space bar anything but a stamped piece of metal; no wood or synthetic space bars are ever seen.  The space bar is small, and tinny-feeling and perhaps (again) as minimal as one can get and still have operability.  This feature though is right in line with the overall design, relying heavily on inexpensive-to-make sheet stampings for the whole body, as did so many other portables of the early era.
National No. 5  /  serial  22935

Tilman Elster collection

This No. 5 machine actually is the second highest serial numbered machine yet found, and considering the number of the machines that have survived today is very surely from the very end of production.  It is assumed quite generally that once Rex failed and the plant became that of Demountable the production of these portables was dropped, although it also should be noted that many of the same interests were involved with Demountable as had been involved with Rex.  By that time, which was 1923, the National and Portex were essentially obsolete machines and would have required exceedingly low pricing to sell at all.  Much better four-bank machines were either on the market or about to appear (Remington Portable, Corona Four respectively) and the three-bank machines in production (Corona, Underwood) clearly outclassed it as well.  It would appear that these machines were only, in final analysis, a very limited success for a rather short span of time from 1917-1923 or 1924 at the latest.
NATIONAL / PORTEX summary - dates, serial numbers

National No. 2; introduced 1916, product of National Typewriter Dept. of Rex Typewriter Co. serial numbers through about 2500

National No. 3; introduced January 1918; National Typewriter Dept. of Rex Typewriter Co. serial numbers roughly 3000 to 14000

National No. 5; introduced January 1920; National Typewriter Co. serial numbers roughly 15000 and up, but see next entry.

Portex No. 5; introduced May, 1922; Rex Typewriter Co. serial numbers roughly 16390 and up, but see next entry.

Rex Typewriter supposedly re-merged the National Typewriter Co. early in 1922 but for some reason National No. 5 and Portex No. 5 machines continued to be produced about evenly in serial number blocks until the end of production; highest serial known is 22540.

Printed reference exists to the sale of the EXPRESS in 1919, which may indicate assembly of earlier spare parts for this purpose.

SOURCES:  Serial number listings courtesy Herman Price, Thomas Fuertig and "The Typewriter: An Illustrated History by Typewriter Topics," originally published 1923.