Here's one of the extremely rare M3 M1911 shoulder holsters marked for the US Navy. This one has been rigger modified, the trigger area has been cut out and the bottom of it has been sewn shut (anyone know why).

Not sure how you can determine it to be rigger modified. Could have been done at any time by anybody to accommodate a revolver.

It was a shame  to do that to an otherwise nice holster.

I saw in another post (maybe on another forum) that the trigger cut out was a common rigger mod, I've seen it on another USN M1911 M3 and a USN .38 M3

https://www.usmilitariaforum.com/forums/index.php?/topic/361607-us-navy-victory-pistol-shoulder-holster/

heres the post I was talking about

The one in the link appears to be  true rigger modified. They tend to be neater and more professional  looking cut rather than just cutting a piece of leather from the holster.

On yours it does not appear to be true rigger modified but rather someone just cutting a piece of leather out to allow a fit to some revolver.

This one is done pretty cleanly done, sewing as well. The aging on the threads and on the cut piece of leather match the overall wear of the holster, so I do believe it is at least period done, perhaps by the Aviator who had to modify it to fit a revolver rather than a 1911

Have to say thats the First USN marked45 holster I have seen. Usually see the BOYT marked revolver holsters. I have a 45 holster with the bullet loops added to the shoulder strap but its not USN marked.

I’ve only seen one other around (with this same trigger cutout mod). I read only 5,000-10,000 of them were procured by the Navy, as they usually used Victory’s