Specifically, this collection contains, "United States Passport Applications from two different NARA collections: M1490, and M1372."
Since there are only 2,320,105 images, it cannot be a complete collection.
I was only able to access records for M1490, and these are only passport applications between the years 1906-1925. It seems like this might be complete for these years. I know that passport requirements for foreign travel were not as strict during this time period as they currently are. Also, these passports can include multiple members of a family.
The big drawback is that so far these records remain unindexed. They are only organized by the date the application was submitted. So, if you happen to know when that was (preferably narrowed down to the month!), and have a lot of patience, you might be able to find a record of interest.
This collection needs to be indexed! You can help! If it is indexed, the records will suddenly become accessible to millions of other people because suddenly you will be able to look up the records by name, residence, birth place, etc.
Here is an example that I found of a person (probably Czecho-German) applying for a passport from Cook County, Illinois.
Look at all the great information you can learn!
"I do solemnly swear that I was born at Uscz [?] in Germany, on or about the 20
day of Apy [April?], 1830, that I emigrated to the United States, sailing on board
the - from Liverpool, on or about the 18 day
of March, 1852; that I resided 54 years, uninterruptedly, in the United States,
from 1852 to 1906 at Chicago, Ill; that I was naturalized as a
citizen of the United States before the Superior Court of Cook Co,
at Chicago, on the 25 day of March, 1862, as
shown by the accompanying Certificate of Naturalization; that I am the IDENTICAL
PERSON described in said Certificate; that I am domiciled in the United States, my per-
manent residence being at Chicago, in the State of Illinois
where I follow the occupation of Manufacturer; that I am about to go abroad
temporarily; and that I intend to return to the United States within six
months with the purpose of residing and performing the duties of citizenship
Sworn to before me this 20 day of March, 1906.
DESCRIPTION OF APPLICANT.
Age, 75 years
Stature, 5 feet, 8 inches, Eng.
"Applicant desires Passport sent to the following address:
159 Randolph St.,
I would LOVE to find something like this about my ancestors! Let's index it and make it happen!