"The First Mustang..." you say?

Depends on how you define "The First Mustang..." because the actual truth may never be known.
The phrase "The First Mustang..." is an oft abused term used everywhere when the words have never been proven out - not by noted and respected historians, rumor spreaders, or two guys at a car show debating the subject.

The words..."The First Mustang..." make the hair on the back of my neck point straight out because it is an unproven distortion of history. The words are pure BS...

Before you is 5F08F100001 - the first Mustang "order" ever. With a consecutive unit number of "100001", it is the first 1965 Mustang order ever for the defuncted Dearborn, Michigan Assembly Plant, which closed in May 2004. It does not make it the "first" Mustang and that's what confuses people.

What does this mean?
Consecutive Unit Numbers for Ford Division cars began with 100001, then 100002, 100003, 100004 and so on. This made 5F08F100001 the first 1965 Mustang "order" or "job number" for the Dearborn Assembly Plant for the 1965 Model Year.

However, "consecutive unit number" does not mean how they were positioned on the assembly line. "Consecutive Unit Number" is the job or order number - not the order they were in on the assembly line.
The order they were in on the assembly line was the ROTATION NUMBER or SEQUENCE NUMBER to where they could be easily located on the line. How this was done gets darned confusing. And that is another subject entirely.
5F08F100001 was not JOB 1 on March 9, 1964. It is believed somewhere between 5FXXX100200 and 5F08F100211 was. March 9, 1964 was the start of MASS PRODUCTION. Anything built prior to that date was considered PRE-PRODUCTION.

I suspect a white or red convertible was the symbolic JOB 1. And THAT is another subject entirely too.
Okay - back to "the First Mustang..." saga. There were actually a number of "first" Mustangs. The prototypes... Hand-built bodies that were nothing more than steel bodies for engineering purposes. Then, fully assembled Mustang prototypes. Then, drivable prototypes. Prototypes erected for a variety of engineering purposes - the fitment of parts, revisions, stampings, and more. There were even crash test prototypes built to be smashed and destroyed. Unknown how many.

It is unknown how many prototype Mustangs were produced - and later destroyed. None would ever be in private hands though you never know what went out the back door - so to speak. Factory records were destroyed long ago.

Then.....there were "Pilot Plant" Mustangs produced at Ford's Allen Park plant just south of the Dearborn plant on something of a mini assembly line to refine how cars are assembled. They were 5SXXX100001 through roughly 100009. There were likely more, but we've never seen a higher Pilot Plant number than 100009.

Early in 1964, Dearborn began producing "pre-production" Mustangs with "05C" date codes indicating their status as pre-production Mustang units. The "05C" date code does not mean they were assembled March 5th. Pre-Production units range from 5F08F100001 through roughly 100180 or lower than 100200. Mustang units with an "05C" date code pre-production Mustangs. They are NOT prototypes. To repeat - THEY ARE NOT PROTOTYPES.

There is a lot of mystery surrounding those first pre-production Mustangs built prior to Monday, March 9, 1964. We may never know the complete truth about them because Ford destroyed production records prior to 1967. There are no photographs of Mustang JOB 1 on Monday, March 9, 1964.

None...
No one has looked more extensively in the Ford archives for JOB 1 than Donald Farr and me. Any images of JOB 1 are gone - likely pirated from the archives or thrown away.

Summing this post up - "The First Mustang" remains unknown. Regardless what has been in print or on the Internet - no one knows to this day. I remain hopeful someone will confirm - and not with phony documentation or word of mouth.