The man kneeling immediately to our left of the vertical pipe in this picture, is wearing a dark coloured star emblem at the top of his left sleeve, the colour shade is consistent with the star being dark red.
U.S. Army 6th Infantry Division.
They are wearing khaki garrison caps which have coloured piping around the top edges of the cap.
Similar caps were in use by the army in WW1 but after WW1 they soon fell out of use, except in the Army Air Corps.
They were reintroduced in 1939 and that version was edged with different coloured piping for the different branches of service,...infantry, artillery, engineers, and so on.
Infantry was light blue, artillery was scarlet.
The edging on the caps of the man in the middle and the two men on our left, look quite dark, so I'm guesstimating that they are artillerymen, and although the unit was called an infantry division, it did have other non infantry components within it.
That coloured edging was discontinued in 1956.
The 6th Division was decactivated in Korea in 1949, it was reformed and served between 1950 and 1956, but it didn't serve overseas during that period.
So the picture is WW2 era, and it's dated between July and August 1943 and they're enroute to Oahu in Hawaii.
https://en.wikipedia.org/wiki/6th_Infantry_Division_(United_...)
I've only viewed a few of the pictures at the moment, and I've seen a couple of the numbers that you mentioned, my guess is that because of their quantity and the various viewpoints involved, those pictures were probably taken by an official unit photographer, or perhaps by a Stars and Stripes photographer.
I suspect that the numbers are file reference numbers that the photographer or a unit clerk gave to the pictures, and it wouldn't surprise me if some of them have a stamp on the back which says something like, property of the U.S. Army or the U.S. War Department or some such.
If anyone wants to challenge, add to, or give a different assessment of that picture, they're welcome to.
**************************************************************
What you have there is much more than just a collection of family photos, it's an historically valuable visual slice of American history, and I'm guessing that not many similar collections have survived.
They deserve to be conserved, preserved, documented, and copied to one or more relevant official photographic, and or historic, archives.
***********************************************************
Go here
http://boards.ancestry.com/topics.Military.wwii.troopshipvoy...and throw this information at a guy called ww2connections aka Richard V. Horrell, who posts on that message board, and there's a good chance that he may be able to tell you what ships transported the unit.
They'll probably be called USAT something or other.
USAT = U.S. Army Transport ship.
Post an enquiry message, and he will see it, include the URL of this message thread.
***********************************************************************
http://tinyurl.com/p8e76qb