> According to R. P. Hunnicutt's ARMORED CAR: A HISTORY OF AMERICAN WHEELED COMBAT VEHICLES, the Ordnance Department designed the T4 and two were built by James Cunningham, Son and Company [in] 1931. After tests at the Aberdeen Proving Grounds, they were standardized as the M1. A total of 20 of these cars were produced up to March 1938. >
That's Hunnicutt's take on things, and while I'm not declaring his figure is wrong, it's the first time I've seen that specific total of 20 units made. I have read as many as 24---a dozen each T4s and M1s---which I pretty much dismiss, because that many T4s is highly unlikely. See the summary arguments here:
The most common total numbers encountered are twelve and fourteen: either ten or twelve purpose-built M1s, along with the pair of T4s, which may or may not have been retro-designated as M1s. There is an interesting photo of a long line of such armored cars, probably at some maneuvers in the 1930s (other vehicles are shown in the background), which I'm presently unable to pull up as an individual image, but see the War Wheels site (third row down, first photo on left). There is a slightly expanded version of this shot out there showing the unmistakable hood of yet another M1, or T4, in the immediate foreground, which makes the total of such AFVs at that site
as thirteen or fourteen. So, it's likely that at least a dozen M1s were purpose-built.
However, a good example for believing other than Hunnicutt's 20 vehicles produced appears here....
....wherein the accounting goes to the number specified in the contract versus that actually built before the contract was cancelled by the army. Before accepting Hunnicutt's figure as gospel, the possibility/probability of the army cancelling the contract after it had found this AFV's off-road mobility disappointing should be seriously considered. After the trials of the M1, the U.S. Army went in the direction of half-tracks, with which Cunningham & Co. had also dabbled during the 1930s. I've looked previously at the numbers of the M1 armored car built, and as I write this, I cannot say if Hunnicutt is right or wrong in his final figure. The answer to numbers most certainly lies at the National Archives---very likely at Archives I downtown---but I've not made that quest.
One thing I do not believe until I get additional proof is that the T4 was strictly an Ordnance Department design. The usual course was for the army to come up with a general notion based on perceived need, and then to send the idea out to bidders for their own designs, based on their industrial expertise. The decision went, presumably, to the best design, which sometimes was that of the lowest bidder and sometimes not, but almost always the final design incorporated the best features from all bids. An atypical story is that of the jeep, with the bidders being Ford, Willys Overland, and American Bantam (the bankrupt and reorganized American Austin Car Company). The most promising design, and also that quickest off the mark, came from Bantam, but it was a small company whose production facilities were limited, at least according to the army, so its superior design was leaked to the two larger firms. Willys won the initial bid and Bantam was swept out of the picture (though during the war it manufactured a relative few updated jeeps, but mostly jeep trailers). Yeah, the exigencies of military need and all that, but the way it went down leaves an unsavory taste.
For those unfamiliar with the precursor to the jeep, here is the original Bantam "Blitz Buggy".
As far as those chrome headlamps on the M1 armored car, I think the ones on the T4 were too small and produced insufficient light, and the larger chrome successors were almost certainly a commercial model installed as the quickest expedient. Or the headlamps on the T4 were specialty items for the army specs whose production could not keep up.
Here are shots showing the headlights on the T4 (one image) and on the M1 (two images).