Farm Collector magazine has done a 2 part story on Caterpillar history. Most is agreeing with what has been posted here over the years. 

The one thing I don't ever remember hearing is another guess for what the R stands for in the RD series of tractors. They are suggesting the R is for Franklin Delano Roosevelt.  I know the subject of the R has been discussed but with the new search that I have not mastered, did I forget or is this a new guess.

I came across that definition a while back--but don't remember where i read it

The "R" was in honor of the engineering work of Art Rosen a Caterpillar Engineer in the 30's and 40's the designer of the D9900 engine which was the first diesel placed in a crawler tractor.

so rosen's diesel.

I was just reading on some designation on some of the newer Cat engines and it seems like it was pretty common to put the head engineers intals in the final product

Here is a page posted by OzDozer on Jan 18, 2009.  Food for thought!!

R designationCategory: DISCUSSION Bernie - Below is a virtual copy of my post from ACME. This version I have supplied is taken verbatim from Henry Howards (VP of Caterpillar Sales in the 1930's) historical discussions with author Randy Leffingwell .. and I believe this is as close as anyone gets to the story behind the "R" designation of the "RD" series Cats ..

"In the period from late 1931 to late 1937 Caterpillar went through a lot of upheaval with a lot of rapid changes .. from the release of the Cat Diesel, to major color change, to nomenclature changes, and a host of new, totally redesigned models.

In 1934, there was an argument put forward by salespeople, led by Henry Howard, Cat VP of sales .. that the nomenclature of Cats had to change from the likes of Sixty, Thirty, 2 Ton, etc. .. which were originally designed to represent HP and weight ratings .. to something more obscure, that didn't really relate to anything.

The problem salespeople had been having in previous years, was that with development, tractors were no longer the HP, or weight, they were originally allocated.

After a considerable amount of heated discussion, it was suggested by Claude Heacock, Cat President, at a meeting, that a new tractor, yet to be named (it became the R5) be named the 'Roosevelt 50' .. !

This appalled the sales people present, in that, it was known that Heacock had a great hatred for President Roosevelt and his Depression policies .. and made no secret of it .. to the extent it had been affecting sales in some areas!
It appears that Heacock had, in a fit of perversity, decided that Roosevelt was a good name, as it meant nothing to him!

The idea was shouted down .. and letters and numbers were discussed .. with the basic ideas of a letter for gas tractors, and another letter for diesels becoming the nomenclature .. as well as the basic size groups, of 4, 6, 7 and 8 ..

Heacock handed down a decision, that from early 1935, gas Cats were to be prefixed with 'R', and diesels with 'RD' .. with the size number behind the 'R' and 'RD'.
This policy was carried out on an ad-hoc basis, as the RD-8 had already been named the '80', and name plates cast with that number .. but they were hurriedly ground off, and replaced with RD-8.

The R4 was released in 1934 with the Thirty name .. and against all stated policy, it stayed the Thirty until 1938, when it finally became the R4.

The diesel engined R4 was released in early 1936 as the RD-4, and the 'R' was dropped from all diesel models in 1937.

No-one knows for sure, except Claude Heacock, why the 'R' in the nomenclature was chosen.
It has been reported that the 'RD' stood for Rudolph Diesel .. who was the original designer of the diesel principle .. but it has also been suggested the link is fanciful, as there was no real tie-up between Rudolph Diesel and Cat, seeing as Diesel died in 1913 under mysterious circumstances.

It has also been suggested the 'RD' stood for Rosen Diesel, as Arthur Rosen was the brilliant young Cat Diesel engineer who first proposed that Cat build their own diesel engine .. as far back as 1923 he contacted Pliny Holt with the proposal .. but it was 1925 before he got a job at Cat, and it was 1927 before he went to work on the design of the Cat diesel, using a Daimler Benz and 4 other current diesels as start point designs.

The largely Arthur Rosen-design Cat Diesel, released in 1931, was an immediate success, and Rosen became a celebrity, producing over a dozen research technical papers on Diesels between 1932 and 1935.

He was also responsible for working with Standard Oil lubrication engineers to produce the first detergent engine oils (Delo), to overcome the serious oil burning, ring sticking and gumming that nearly killed the early diesel sales.

As I have said .. no-one knows, except Claude Heacock, why R, RD and D were the chosen letters .. but it sure produces some conjecture .. and the reasons have been forever lost with him, as he is now long dead."

Thanks for sharing, quite interesting read. In reading the Standard Oil DELO, Was that an acronym for Diesel Engine Lubricating Oil? Hence, Delo? JM

Thank you Jim for finding that. I knew it had been determined that the R was not ever explained with 100% confidence.

Interesting history!
I find it sad that the apt name "Caterpillar," a crawling creature, was allowed to devolve to "Cat," although kitties do crawl at times as in stalking a mouse, but it's just not the same.
To me, the name Caterpillar evokes that distinctive engine roar and track clanking. Cat, not so much.

Ok, here we go, lol, The name Caterpillar came from a photographer back in the mid twenty's that was photographing a merging Best and Holt company crawler when the he said "It crawls like a caterpillar", thus the name stuck. There may be some more details about it but basically this is how it was determined.